Former Vice President Joe Biden and Senator Elizabeth Warren joined striking General Motors workers on picket lines Sunday. Biden was in Kansas City, Kansas, while Warren was with workers in Detroit.

The nationwide walkout isn't just about the terms of a new contract, but rather about big changes down the line. Negotiations continued this week at a Detroit hotel, where difficult questions are demanding difficult answers about the future of the auto industry and its workers.

"How many jobs will exist because of electric vehicles, autonomous vehicles, automation? Those are issues of real concern for the far out future," said Michelle Krebs, an executive analyst at Cox Automotive.

Electric vehicles — still an unusual sight on the nation's road — are gathering momentum. GM plans to introduce 20 new, all-electric models by 2023, a major, if still uncertain, step away from gasoline or diesel power.

Electric batteries and motors are much simpler to make than the internal combustion engines powering most cars today. They require only a few hundred parts instead of thousands. That means fewer workers on the factory floor, and fewer workers needed to keep the vehicles running once sold. Which in turn means fewer profits for dealerships and their mechanics.

And yet, along the picket line, United Auto Workers member Karen Huffman thinks there's a bright spot.

"You're always going to need people to build vehicles," she said. But analysts believe the coming transformation is undeniable.

"We know that eventually electric vehicles, autonomous vehicles, new ways of us acquiring personal transportation is going to happen," Krebs said. "We don't know when that will be and we certainly don't know when anyone's going to make money on it."

Big questions in need of answers, and not just for autoworkers.