A caution: These polls were conducted in a rapidly developing news environment, sometimes over only a single day of interviews. This poses challenges for pollsters, who have fewer opportunities to call back hard-to-reach respondents. It could also mean that the surveys were conducted at a moment when Democrats or Republicans were particularly eager to participate in polling. Many pollsters refuse to conduct one-day surveys altogether. And these particular pollsters have tended to show more support for impeachment than others over the Trump presidency; they may continue to do so today.

Even if the polls are perfectly representative of today’s public opinion, they are just a fleeting marker at the beginning of a long process.

The increased support for impeachment was driven by Democratic-leaning voters and longtime opponents of the president, many of whom have long been skeptical about whether impeachment is worth it if it poses political risks to Democrats or if the president won’t be removed from office.

It is not clear whether Democratic-leaning voters are rallying behind Ms. Pelosi and other Democrats, or whether they consider the Ukraine allegations to be materially worse than those reported during the Russia investigation.

If the figures are matched by other surveys, it will suggest that support for impeachment is fairly similar to the opposition to Brett Kavanaugh’s nomination to the Supreme Court last year. For Democrats, this level of support would probably be enough to avoid the most severe political costs they’ve long feared from pursuing impeachment. But few congressional Republicans would feel much pressure to distance themselves from the president.