For an object lesson in how venomous American politics has become, look no further than the insults hurled in our direction late last month. We’re two millennial women who work at No Labels, a political reform movement founded in 2010 featuring Democrats, Republicans and independents working together to solve America’s toughest problems. In March, No Labels organized in support of Rep. Dan Lipinski, a moderate Democrat from Illinois whose primary challenger had been endorsed by a host of liberal interest groups.

After Mr. Lipinski narrowly won, the president of Naral Pro-Choice America, Ilyse Hogue, accused No Labels of following President Trump into “bigotry.” When our group tweeted that Mr. Lipinski’s victory showed “America’s political center is finally striking back,” Howard Dean, a former chairman of the Democratic National Committee, replied: “This is foolish nonsense.” Former Obama speechwriter Jon Favreau complained that Mr. Lipinski had also voted against the Affordable Care Act and opposed same-sex marriage: “To call people who disagree with those positions the far left is a f— embarrassment.”

We don’t agree with Mr. Lipinski on every issue either. (Hey, Ms. Hogue, turns out we’re pro-choice, too.) But Mr. Lipinski still votes with his party 88% of the time. That hardly makes him a turncoat. Moreover, we think there’s a bigger problem in Washington than whether Mr. Lipinski passes any given group’s political litmus test.

Legislators in both parties have to worry too much about primary challenges from ideologues on the far left or far right. That’s why Democrats and Republicans are so unwilling to work across the aisle. And that in turn is why Congress is failing to address the biggest problems facing America.

Here’s a specific example. When the individual insurance market almost imploded last year, the far left (which wants a single-payer system) and the far right (which would be happy enough to watch ObamaCare’s exchanges collapse entirely) went straight to their respective ideological corners. They ignored the concerns of the ordinary Americans who stood to lose their medical coverage.