The gap between Jonas Vingegaard and Tadej Pogachar is still just 17 seconds as the Tour de France passes the halfway point.

Vingegaard has the jersey, but Pogachar has the momentum. Pogachar has the individual skill, but Vingegaard has the team. In other words, any argument in favor of one side can find a persuasive counterargument in favor of its rival.

When Vingegaard tries to tip the balance of this eternal debate, especially if the race returns to the high country with a summit finish at the Grand Colombier on Friday prior to a weekend doubleheader in the Alps, perhaps the most valuable mountain domestique in pro cycling, Sepp Kuss, will be a key factor.

The American has already shown his talent by flirting with Vingegaard's frenetic attack on the Col de Marie Blanc to Larns on stage 5 and then slicing through the yellow jersey pack on the Col du Tourmalet the following afternoon. After breathless races in the Pyrenees and Massif Central, Cous believes the Tour will enter a new phase at altitude this weekend.

"I think the Alps will make a big difference as fatigue sets in," Kuss told reporters in Clermont-Ferrand before stage 11. 'There will be more climbing throughout the stages, that's for sure. Up until now, it's been more or less explosive. So I think with the added fatigue and multiple mountain stages, it's going to be a different race."

Twelve months ago, Pogachar slightly outpaced Vingegaard in a punchy opening weekend, but on the Tour's toughest mountain stage, the Dane decisively outpaced Vingegaard. While many in the peloton would disagree with Kuss's assertion that "the Tour has yet to face a real mountain stage," the fact remains that the grueling three days at the end of the second week are a different kind of test than what Pogachar and Vingegaard have faced so far.

"They've been evenly matched so far, but as I said before, there's no real alpine stage yet. I think Jonas feels comfortable there and is looking forward to it."

Such terrain is, of course, where Cus is at his best. At the Giro d'Italia in May, for example, his pace-making in Monte Bondone defined the race, and when Roglic arrived in Rome five days later in the pink jersey, Cus became the fifth rider to lead his Jumbo-Visma teammate to overall victory in a Grand Tour.

Kuss' role is familiar, but the combination of Giro and Tour is new. He was late to join Roglic's support role in Corsa Rosa due to Wilco Kelderman's injury, but his importance to Vingegaard's cause means that he is the only Jumbo-Visma rider to line out in both Italy and France this summer.

"So far so good. I think the Giro was good preparation for the Tour," Kuss said. I'm still in the rhythm of racing in the Giro, and we've done some long stages, so it's been good endurance training and interval training. So far so good."

Indeed, as the Tour enters the second half of the race, Kuss is still in 10th place with 6:45 to go. While his key task remains to ride the high mountains as the final Sherpa in the Vingegaard, his overall ranking has strategic value in the early climbs, where the pack is likely to break up over the weekend.

"When the start is very difficult, given my current position on GC, a good move can always be used to attack or climb. It definitely comes in handy when it gets crazy with these uphill starts," Kuss said.

"You never know what the situation will be and if it will help someone ahead of you. On paper, I think the priority is to focus on Jonas, but races can take strange turns."