A third party signed up 15,000 voters in Arizona. Democrats worry that’s enough for a Biden spoiler

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...