A May 16 survey by Public Policy Polling, a partisan Democratic firm generally rated as credible, found that the pro-impeachment numbers for Trump had shot up to 48 percent, with 41 percent opposed.

What does the future hold?

As long as Republicans and Democrats are “pulling with roughly equal force,” Nate Silver observes at the website FiveThirtyEight,

Trump isn’t going to be removed from office, which would require a two-thirds majority in the Senate. But if something snaps — if Republicans have reason to think Trump has become a liability even in red states — look out.

Although Democrats are by no means unified on the issue, much of the activist base of the Democratic Party smells blood. At least 23 House Democrats and three Senators have signaled that they are receptive to impeachment, most prominently Representatives Al Green of Texas and Maxine Waters of California, who have called for the start of formal proceedings. Matthew Yglesias, a liberal columnist, wrote “The case for impeaching Trump — and fast” on May 22 on Vox. Brian Buetler wrote in the New Republic on the same day, “Democrats Should Proudly Call for Trump’s Impeachment.”

The subhead on the Yglesias essay reads “This is the exact situation impeachment was meant for. Let’s hurry up.” Yglesias goes on:

A slow, ugly, painful divorce only means that Trump’s sins will more and more become the sins of the entire party, and impeachment will look like less and less of an appropriate remedy for wrongdoing that can only be redeemed by a broad and deep electoral landslide.

Buetler, in turn, favorably quotes Waters, who disagrees with those who say that it is too early to begin impeachment proceedings: “No. We can’t wait that long. We don’t need to wait that long. He will have destroyed this country by then.”

So far, these arguments have not been persuasive to top Democrats in the House and Senate. Nancy Pelosi, the minority leader, told reporters at her regular press briefing last week:

I hope some would curb their enthusiasm until we have all of the facts and have confidence that when the American people understand what is there, whether it’s grounds for impeachment or grounds for disappointment, then they’ll know.

Similarly, Dick Durbin, the Senate Democratic whip, told reporters that he has “been talking to the base since November the 9th and telling them this is a marathon, it’s not a sprint.” He went on:

We have an orderly process in our government. We’re going to follow it. They don’t like to hear it, but I think that’s the facts.

The caution displayed by Pelosi and Durbin is widely shared among Democratic elites.

Robert Stein, a professor of political science at Rice University, was more explicit in an email:

At present the case for impeaching the President is constitutionally insufficient and politically dangerous for Democrats. That is, most Republicans and weak and strong supporters of the President would believe impeachment at this time to be solely political in origin.

Stein continued:

Under these conditions impeachment would be framed by the President, his supporters and Congressional Republicans as a coup d’état to reverse the outcome of the 2016 election and the policies on which President Trump and the Republican Party campaigned.

The real test for impeachment, Stein argues,

is if new information from the special prosecutor or Trump himself erodes support among those who voted for him in 2016.

A tiny faction of House Republicans — Justin Amash of Michigan, Carlos Curbelo of Florida and Walter Jones of North Carolina — has warned that the sum of the allegations against Trump, if proven true, could be grounds for impeachment.

A House vote to impeach the president requires a simple majority, 218 votes. Given the current composition of the House, 25 Republicans would have to join the 193 Democrats to impeach Trump and of course that calculation assumes Democratic unanimity, which is far from certain.