Perhaps Democrats learned more than one lesson from their faceplant over the weekend. According to the New York Times, leading Democrats have begun leaning on their billionaire funder to dial down impeachment talk. They’re worried about the extremist tilt in which Tom Steyer might take the party — and the incumbents he’ll force them to protect:

Democratic leaders have pressed Tom Steyer privately, urging him to tone down his campaign calling for President Trump’s impeachment. They have prodded him in public, declaring on television that they consider impeachment an impractical idea. And party strategists have pleaded with Democratic candidates for Congress not to join in.

But Mr. Steyer, a California billionaire and one of the Democratic Party’s most prolific donors, has only intensified his attacks in recent weeks. Buoyed by tens of millions of dollars in television commercials — financed out of his own pocket and starring him — Mr. Steyer has become one of Mr. Trump’s most visible antagonists, firing up angry Democrats and unnerving his own party with the ferocity of his efforts.

Mr. Steyer is likely to unsettle national Democrats further in the coming weeks, with a new phase of his campaign aimed at pushing lawmakers in solidly liberal seats to endorse impeachment. Having collected more than four million email addresses from people who signed an impeachment petition, Mr. Steyer has begun prodding those voters to call congressional offices and lobby them for support.

Democrats have distanced themselves from Steyer’s strange crusade for a while — publicly, anyway. DNC chair Tom Perez heaped praise on Steyer two months ago but got a case of laryngitis when it came to his impeachment push.  At about the same time, Steyer admitted that he doesn’t have much of a case for removing Trump, but that the lack of grounds won’t stop him from demanding that Democratic candidates toe the line on supporting impeachment. Steyer made that litmus test clear last October.

Perez, Nancy Pelosi, and other national party leaders have issued public statements saying that impeachment isn’t on the front burner, but they haven’t exactly shrugged it off until now. They need the activist base engaged in the effort to take back the House by generating turnout in battleground districts to push Republicans out of the majority. Until now, they’ve had no problem playing footsie with Steyer and the radicals. However, as the NYT’s Alexander Burns reports, Democratic leaders have discovered that Steyer is serious about that litmus test, too. He’s rallying progressive activists to his cause and threatening primary fights against Democratic incumbents who won’t demand impeachment, which will threaten Democrats’ ability to convince swing voters that they’re normal enough to trust:

While Democrats intend to run on a fiercely anti-Trump message this year, party leaders envision a campaign of broad attacks on the president’s economic agenda rather than a blunt-force impeachment pledge. There is no realistic chance of impeaching Mr. Trump while Republicans control Congress, and Democrats from moderate and conservative districts fear the idea could alienate voters otherwise likely to vote their way in November.

But the Democratic base, enraged by Mr. Trump and frustrated by party leaders counseling restraint, appears enthusiastically open to seeking the president’s removal.

The problem is that the Democratic “base” largely exists in small geographic areas, mainly centered on the coasts and in urban cores. Democrats don’t have any trouble winning elections in those areas — they already hold those seats in Congress. Running an election on the explicit agenda of undoing the previous vote might sell well in those areas, but it’s going to reinforce the image of a radical Democratic party everywhere else.

And right now, the party is already dealing with that problem. Chuck Schumer overplayed his hand on DACA and took government and CHIP hostage to force a deal on his own extreme terms for dreamers. In the red states where Democrats need to pick up seats (and protect others, especially in the Senate), Republicans are killing them with messaging over the shutdown. If that played poorly for Democrats, imagine how impeachment will play on the campaign trail.

Party leaders should be concerned about Steyer, but they’ve normalized him for too long to do much about it now. It’s far from certain that Democrats would succeed in taking control of the House without Steyer, but he might just be the man who snatches defeat from the jaws of victory in November.