LUSAIL, Qatar - Momentum is a fickle force at this stage of a Formula One world championship.
Rewind two weeks to the Monday after the Mexican Grand Prix and momentum promised to carry Max Verstappen to his first F1 title. Return to the present day, and it has swung behind Lewis Hamilton off the back of two dominant wins in Brazil and Qatar and looks set to deliver a record-breaking eighth world championship.
In truth, the 2021 title battle hangs in the balance. With two races remaining, Verstappen leads Hamilton by eight points in the standings after conceding 11 at the last two races. If current form holds true, Hamilton will win the title. If it teeters just slightly in either Saudi Arabia or Abu Dhabi, it will be Verstappen's.
The two most recent races in Brazil and Qatar have undoubtedly suited Hamilton's Mercedes car. So much so that the performance of Verstappen's Red Bull looked unrecognisable from one week in Mexico to the next in Brazil.
Such dramatic swings in performance tied to such huge consequences in the championship inevitably lead to suspicion and accusations. Both are natural -- and unfortunate -- byproducts of a competitive title run-in, and they have only been amplified in recent weeks by the intensity of holding three consecutive race weekends across three different continents.
In Qatar, where the triple-header was capped off by a commanding Hamilton victory, Verstappen's Red Bull team undoubtedly wobbled. From a points perspective, the weekend was a relative success, with Verstappen minimising the loss to Hamilton in the drivers' championship with second place while Red Bull closed the gap to Mercedes to five points. But off the track, the battle cries coming from the Red Bull camp sounded increasingly desperate.
The war of words between team bosses Christian Horner and Toto Wolff has provided a consuming subplot to the 2021 season, but also an insight into the confidence each team holds an any one time. Hearts are worn on sleeves alongside Swiss watches and tech sponsors in F1, and it's common for emotions to overflow. In Qatar, the battle of the bosses hit a new height, leaving Red Bull looking bruised but not quite beaten.
Horner notched up an early victory in the race weekend when, on Friday, the FIA denied Mercedes' request to review an incident between Verstappen and Hamilton in Brazil. The two drivers went wheel-to-wheel into Turn 4 on lap 48 of the Sao Paulo Grand Prix, only for Verstappen to leave his braking too late and force Hamilton wide.
Horner correctly predicted Mercedes' case for a review of the incident would not satisfy the requirements set out by the FIA. New evidence, in the form of previously unseen footage from Verstappen's onboard camera, was not be considered "significant" enough to reopen the case, meaning the move stood as a "racing incident".
The timing of Horner's vindication could not have been more sweet for Red Bull, as the stewards' decision dropped midway through a televised news conference in which he was sat alongside Wolff. The Mercedes man attempted to shrug it off, but this was an early win for Horner.
Yet the Red Bull team boss was intent on diverting the focus away from his driver's actions in Brazil and towards the legality of Mercedes' car. Convinced Hamilton had a straight-line speed advantage from a flexing rear wing in Sao Paulo, Horner took the opportunity to point out "score" marks on the inside of the Mercedes' rear endplates.
Red Bull's theory was that these marks were a result of the main plane of the rear wing flexing under aerodynamic load, which in turn reduced drag, increased top speed and explained Hamilton's apparent speed advantage in Brazil. It was a serious accusation as flexible bodywork that can be construed as a moveable aerodynamic device is outlawed under F1's regulations. Wolff hit back the next day by saying Horner was "chasing ghosts", but the comments were enough to cast doubt over the legality of the Mercedes in the build up to the race.
On Saturday evening, the wing passed a newly introduced deflection test set by the FIA as part of a "fact finding" mission for next year's regulations. Flexible bodywork is likely to be a major battle ground under F1's all-new regulations for 2022, and the introduction of the test in Qatar, which includes a more stringent load test on the rear wing main plane, doubled as a bellwether for Red Bull's accusations.
As well as passing the test, detailed photos from alternative angles of the Mercedes rear wing suggested the apparent scuff marks may in fact a different weave of carbon fibre in the construction of the endplate. Two different weaves on the endplate where the main plane joins it could, under certain light and at certain angles, look like marks against the surface of the carbon fibre.
On race day, Horner was satisfied the speed differential between Mercedes and Red Bull was back in line with expectations, even though Red Bull still appeared to have a deficit of around 8 km/h to the Mercedes. Red Bull had suffered rear wing issues of its own in Qatar during practice when the rear wing's DRS flap oscillated when open. The problem had been observed at a number of previous rounds during practice sessions, but rather than repair the wing as it had done in the past, Red Bull fitted a larger wing with more drag and downforce in Qatar for qualifying and the race.
The swap of Red Bull's wing specification slightly skewed the picture from the outside, but after two days of claiming Mercedes' rear wing was suspicious, Horner changed his tune on Sunday night.
"I think that it is now well policed and the tests that have been introduced should eradicate any ability to circumnavigate [the rules]," Horner said. "I think what we have seen at recent races [before Qatar] was a significant increase in straight-line speed.
"Toto has been at pains to point out that they have gained straight-line speed but nothing has changed, so it's encouraging that this is the first race since prior to Silverstone that we have been able to match them for straight-line speed and, as I said, it's been exponential at recent races."
Mercedes maintained throughout the Brazil weekend that any gains in straight-line speed came from the introduction of a fresh engine rather than any rear wing trickery. Hamilton took a five-place grid penalty at Interlagos in order to introduce the fresh engine into his pool of usable engines for the remainder of the year, but in Qatar Mercedes decided to use an older, less powerful unit. Chief trackside engineer Andrew Shovlin said the new engine would return in Saudi Arabia.
"There are two engines that we are racing, and here [in Qatar] we had the less powerful of the two in the car, due to the nature of the circuit," Shovlin said. "If we look at the track in Saudi, I think it should suit us - for Lewis, we have got the more powerful engine to go in the car, so that should give him a useful boost."
We may never know if there was any truth to Horner's accusations about Mercedes' rear wing, but the balance of evidence seems to suggest they were misplaced. If Mercedes regains its straight-line speed advantage in Saudi Arabia they may resurface, but Mercedes will no doubt point to the return of the fresh engine.
Horner's weekend could have ended there with a semi-debunked accusation and six lost points in the drivers' championship. However, on Verstappen's final lap in qualifying, the championship leader failed to observe double-waved yellow flags at a marshal post on the outside of the final corner and was hit with a five-place grid penalty.
The penalty moved the Red Bull from second on the grid, alongside Hamilton on the front row, to seventh, behind the second Mercedes of Valtteri Bottas (who got a three-place penalty for ignoring single-waved yellow flags). Horner argued against the decision, saying the flags were being waved by a "rogue marshal" who was working at odds with the central marshalling system, which was not showing the sector of track as yellow on the team's data.
Singling out the marshal and suggesting he had acted incorrectly, when he was in fact reacting to Pierre Gasly's AlphaTauri stopping on track in front of him, did not go down well with the FIA. Race director Michael Masi referred Horner to the stewards, who summoned the Red Bull boss after the race and issued him with a warning for breaking the FIA's International Sporting Code. Horner apologised to the marshal in question and offered to join an FIA stewarding course next year as a peace offering. It was an embarrassing end to a difficult weekend.
Asked on Sunday evening if he regretted any of the events in Qatar, Horner said: "No not at all."
"I believe in my team, I'm a straight talker and I've always conducted myself in that manner. I'm not an overly emotional person and I don't rant at cameras.
"I think the way I have conducted myself, I've got no issues with and I would do exactly the same. I think the only issue was regarding any marshal and if there was any personal offence taken for referencing a rogue yellow flag and it was not intended to be aimed at any individual or marshal.
"I don't know if you heard the interview I gave this morning, but I didn't think it was unreasonable."
Say what you want about Horner, but he won't back down. Red Bull hardly covered itself in glory in Qatar, but Horner will not go down without a fight.
"It's going to be tight," he said. "The next track arguably should favour Mercedes and Abu Dhabi, with the modifications made [to the track] there, who knows?
"We've been round the world over the last three weekends and we have pretty much finished where we have started with the points difference. It's that close, it's incredibly close.
"Mercedes have got a very quick car at the moment over the last two weekends. In Mexico, the pendulum was with us, in Austin there was nothing to choose between the two and I'm glad to be taking an eight point advantage into the next race.
"So we have just got to do the best that we can to maximise our chances. I think I said at the beginning of this championship that it would go all the way to Abu Dhabi and I haven't changed my opinion."
Meanwhile, Mercedes considers itself on a roll and is determined to keep it going to the final race.
"I think I never stopped believing that this was on, because we had such a strong race in Turkey before it obviously fell back below our expectations in Austin and in Mexico," Wolff said. "Anyone in the team refuses to give up. I'm grateful how the championship has swung.
"If you had told me at the start of the year that we'd be right in the fight in Saudi and Abu Dhabi I would have taken it. I hope that's going to go all the way to the end and whoever will win merits the win."