More than 15,000 people in Arizona have registered to join a new political party floating a possible bipartisan “unity ticket” against Joe Biden and Donald Trump.

While that’s less than the population of each of the state’s 40 largest cities, it’s still a number big enough to tip the presidential election in a critical swing state. And that is alarming people trying to stop Trump from winning the White House again.

The very existence of the No Labels group is fanning Democratic anxiety about Trump’s chances against an incumbent president facing questions about his age and record. While it hasn’t committed to running candidates for president and vice president, No Labels has already secured ballot access in Arizona and 10 other states. Its organizers say they are on track to reach 20 states by the end of this year and all 50 states by Election Day.