The high level of support suggests that, at least for now, Democrats are on firm political ground in examining Mr. Trump’s attempt to have Ukraine’s president investigate a political rival’s family. Many voters seem to be taking the allegations against Mr. Trump seriously, and they may eventually determine that his conduct merits removal from office.

But for now, many of the voters who support an inquiry have not reached that conclusion. Polls asking whether voters support impeaching Mr. Trump and removing him from office show far more mixed results. The same Washington Post/George Mason University survey found that 49 percent supported removing Mr. Trump from office, while 44 percent opposed. And other recent polls, including one from NBC/WSJ, suggest that fewer Americans support impeaching and removing the president than not. Question wording, question order or even the timing of the survey in a rapidly unfolding news environment could explain the differences.

On average, voters appear to support impeaching and removing the president by a narrow margin, 47 percent to 44 percent, in polls conducted over the last 10 days.

It’s hard to say what level of political support for impeachment might begin to change the political calculus for members of Congress. There are very few precedents for impeachment, and the factual merits of the case against the president could be just as important as the politics.

But it’s safe to say that the current political environment will not do much to pressure Republicans. Since the Pelosi announcement, the president’s approval rating has slumped to 42.8 percent from 44.3 percent among likely or registered voters, according to FiveThirtyEight. But this merely brings his ratings back to where they were on Sept. 10, and well within the normal range for the president since the end of the government shutdown in January.