House Minority Leader Nancy Pelosi, left, and Chicago Mayor Rahm Emanuel, center, have both cautioned their party against impeaching President Trump. (The Washington Post)

Chicago Mayor Rahm Emanuel says the constitutional requirement for impeaching President Trump hasn't been met. House Minority Leader Nancy Pelosi's office says she's not on board with the idea. And former Senate majority leader Harry M. Reid is telling his fellow Democrats to “stop it.”

Good luck with that.

As Democrats drift closer to possibly winning back the House in the 2018 election, one of the big questions is what they would do with that power — and specifically, whether they would use it to try to impeach Trump. Republicans have played up this possibility, believing that even the specter could rally the GOP base and sour Americans on the idea of a transfer of congressional power. Democratic leaders have been quieter, not promoting it but not exactly playing it down, either.

That appears to be changing. If you had to name the three savviest political operators in the recent history of the Democratic Party, they might well be Emanuel, Pelosi and Reid. And this week, all three have thrown up stop signs.

“The less we talk about impeachment, the better off we are,” Reid said bluntly in a just-released NBC News interview.

The problem is that the base has already largely made up its mind. And these Democratic leaders are effectively telling their party not to do the thing that their party very much wants to do.

A January poll from Quinnipiac University showed 76 percent of Democrats said they want to initiate impeachment proceedings against Trump if they win the House. Only 20 percent agreed with Emanuel, Pelosi and Reid.

A Marist College poll last week, meanwhile, showed that 70 percent of Democrats said they would definitely vote for a candidate who wants to impeach Trump.

The real danger is the other side of the coin in that Marist poll. Independents are more likely to say they would definitely not vote for a candidate who supports impeachment (47 percent) than to say they definitely would (42 percent). Republicans oppose it more strenuously than Democrats support it, with 84 percent saying they would definitely oppose such a candidate. Even 1 in 5 Democrats say they would definitely vote against such a candidate.

Democrats have a clear edge on enthusiasm and with middle-of-the-road voters on the generic ballot right now, and this is the kind of thing that could rile up unmotivated Republicans and make independents think Democrats are overreaching. Why mess with success?

And even beyond 2018, it could inject a potentially unhelpful variable into a 2020 campaign in which Trump is most likely to be an underdog. Former president Bill Clinton's impeachment shows us exactly what impeachment can do for a president's stock; his approval rating hit a record high after he was impeached.

But this also comes at a time in which leading Democrats are increasingly giving into their base's, well, base-r instincts. Single-payer health care. A big minimum-wage increase. Even a jobs guarantee now. The 2020 Democratic primary is already looking like a race to the left, and the easiest way to make sure nobody gets to your left is to support things like impeaching Trump. Once one candidate does it, the other candidates will feel pressured to follow suit. And how can you really say no to something three-quarters of your party supports?

Also feeding the beast is the steady drip, drip, drip of developments in special counsel Robert S. Mueller III's investigation, along with Trump's apparent desire to affect its course in the name of self-preservation. Whether that rises to the level of obstruction of justice, we don't know yet, but it's not difficult to see why Democrats might catch impeachment fever if and when Mueller's report goes public. Plenty of Democrats wanted to impeach President George W. Bush over the Iraq War, and plenty of Republicans wanted to impeach President Barack Obama; this is a much more logical pretext for doing it — and a much more difficult set of circumstances to dismiss as not-impeachable if you're a Democratic leader.

With all of that conspiring to push impeachment to the fore, these Democratic graybeards seem to be trying to stop this before it becomes too much of a thing. Thus far, the impeachment push has been led by a handful of Democratic House members and billionaire Tom Steyer, whose combination of vast resources and political debutantism has long rankled strategy-minded Democratic leaders such as  Emanuel, Reid and Pelosi.

The very justifiable fear is that Steyer and his ilk will spawn something much larger, and Democratic leaders will have been caught flat-footed. We're about to find out just how powerful the Democratic base actually is.