Thus far, almost every announced or speculative Democratic presidential candidate has endorsed Medicare for All. However, both Roll Call and The Hill report that the momentum for socialized medicine only grows in the theoretical sense. Now that Democrats can actually pass an M4A bill on a simple majority in the House, suddenly fewer Democrats have signed up to sponsor the effort:

The single-payer “Medicare-for-all” bill that House Democrats are releasing Wednesday seems like it should stand a good chance of attracting more support than last year. After all, the House Democratic caucus ballooned this year and health care concerns were a key factor in the party’s electoral success.

But Rep. Pramila Jayapal of Washington, who will introduce the bill, said 107 House Democrats are initially supporting the measure. That number is fewer than the 124 Democrats who had formally backed an earlier version of the measure by the end of the last Congress.

Last year, a record 62 percent of Democrats backed the House single-payer “Medicare-for-all” bill. Roughly 46 percent of House Democrats have so far signed onto the measure to be unveiled Wednesday.

The downturn in support reflects in part the risks for any politician that proposes dramatic change and uncertainty in a system that is central to Americans’ well-being. It underscores the political calculations Democrats face now that the party controls the House and hopes to capture the White House in the 2020 presidential election. And as the party gains power, its ideas will be taken more seriously.

Translation: It’s a lot easier to posture when you have no access to actual governance. (For historical reference, see “Republicans and the ObamaCare Repeal 2010-16,” “Republicans and The Wall 2008-16,” “Democrats and Immigration Reform 2003-8 and 2011-present,” etc.) It’s all well and good to chant socialized-medicine mantras until someone has to take a vote they might actually win. And then what?

Then, centrist Democrats warn, their majority might prove very very temporary:

Centrist Democrats who helped their party win back the House majority with victories in key swing districts last fall are sounding the alarm that the liberal push for “Medicare for all” could haunt them as they try to defend their seats and keep control of the House.

Instead, these moderates — many of whom will face tough reelection bids in 2020 — are pressing their party leaders to work with President Trump and Republicans to deliver to voters back home a bipartisan victory on lowering prescription drug prices and other health efforts rather than focus on an aspirational Medicare for all messaging bill.

Already, Republican campaign operatives are trying to paint Democrats with a broad brush, linking vulnerable lawmakers in conservative-leaning districts with liberal colleagues pushing for a single-payer health care system. A new poll out Tuesday revealed that 64 percent of voters surveyed believed that Democrats back socialism.

“We’ve got extremists who want to shoot the moon. Some policies would be wonderful, but you’re not going to get them out of the Senate and you’re not going to get them out of the White House,” said one House Democrat who represents a district won by Trump in 2016 and who wants the new Congress to tackle drug pricing first.

Why do almost two-thirds of voters think Democrats back socialism? Maybe it has something to do with the fact that they’re being led on policy by a self-professed socialist in Bernie Sanders, and on tone by another in Alexandria Ocasio-Cortez. This isn’t rocket science, folks.

Usually, political parties have to fight the urge for overreach mainly when they control both chambers of Congress, and especially when combined with the White House. The normal limiting factors of legislation incentivize caution in the circumstances Democrats have now, controlling the House on a slim majority and nothing else. Furthermore, they have other incentives which should be pushing them toward the center: a relatively unpopular Republican president operating under a constant cloud of scandal. The main mission of the opposition in those circumstances is don’t be crazy.

Not only will that damage all the freshman who just got elected over issues with Trump, bills such as M4A don’t have a prayer of advancing anyway. That will leave dozens of vulnerable incumbents twisting in the wind, one war or another. If they vote for a $3 trillion per year program that will strip them of medical-care choice, their voters will abandon them. If they vote against it, it provides progressive activists a pretext to recruit leftists for primary challenges to these first-termers next year, a move that will all but guarantee a GOP majority in 2021.

And when that happens, activists in the Democratic Party will insist they lost by not being crazy enough. That pattern also has a long tradition. Trust me on that one.