It’s therefore tricky to identify the trigger for a surge in support for an impeachment inquiry, but it’s not tricky to identify the surge itself. From the point at which all of that happened onward, there was a significant jump in support not only for an inquiry but for impeachment itself.

The trend over the course of the year looks like this, according to FiveThirtyEight’s average of polls.

On Tuesday, CNN and its polling partner SSRS released another point of data for that chart. According to their new poll, half of respondents think Trump should both be impeached (by the House) and removed from office (by the Senate). That generally matches a poll out on Monday from PRRI, which found that 51 percent of respondents supported impeaching and removing Trump.

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In each case, support for impeaching and removing Trump was up from before the impeachment inquiry itself began. In May, CNN found that 41 percent of respondents supported impeaching and removing Trump from office. In mid-September, PRRI found that 47 percent of respondents supported ousting the president.

CNN had a poll between the May poll and its new one. That poll was conducted at the end of September — after the inquiry began — and found that 47 percent of respondents supported removing Trump. In other words, over the past few weeks, overall support for removing Trump has not actually increased significantly in CNN polling, moving from 47 percent to 50 percent, a shift within the margin of error.

It raises the question, then: Did support for impeachment and removing Trump spike after the inquiry launched as part of a steady upward trend? Or did it just jump to a new level where it will sit?

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The graph above shows a quick surge in support for either impeaching or impeaching and removing Trump followed by a slower increase in support over the past week or so. (From Sept. 24 to Oct. 13, support for impeaching or impeaching and removing Trump jumped 10 points. Since then, it has increased by only 0.3 points.)

A number of polls (using a number of different questions) have spanned the period before and after the inquiry began. While each pollster shows an increase in support for impeaching and removing Trump since late September, the increases since the first post-inquiry polls have been modest. CNN saw an increase of three points. Quinnipiac University’s last two polls show an increase of a point. YouGov’s polls with HuffPost and the Economist recorded increases of one and three points, respectively, since their prior post-inquiry polls.

This is an important question for Democrats for perhaps obvious reasons. Much of the support for impeaching and removing Trump comes from Democrats; support among Republicans remains low. In fact, in CNN’s most recent poll, support from Republicans plunged. In other polls, that support has been flat — but it has consistently been only a small fraction of the Republican base.

Why do Democrats care? Because removing Trump from office necessitates support from at least 20 Republican senators, assuming the Democratic caucus remains united in support of the move. And getting 20 Republican votes in the Senate almost certainly means some semblance of support among Republicans.

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Instead, Republicans tend to see the impeachment inquiry as partisan. CNN’s new poll shows that members of each party see the other party as insincere in its response to the inquiry. Nearly 9 in 10 Republicans say that the inquiry exists because congressional Democrats are out to get Trump at all costs; only 8 percent think Democrats actually believe Trump committed impeachable offenses. Eight in 10 Democrats think congressional Republicans oppose an inquiry because they are committed to protecting Trump no matter what. Only 10 percent think that Republicans actually believe Trump did not do anything impeachable.

Independents, meanwhile, generally track a bit lower than overall support for impeachment and removal. In CNN’s new poll, half of independents support removal, but that’s high for recent polling. It may be a function of an uptick in support; it may be an outlier poll; it may be that the late-September poll was an outlier with unusually low independent support. More polls will offer a better sense of how things are moving.

It’s important to consider this question in the broader context of polling over Trump’s presidency. FiveThirtyEight’s consideration of the impeachment question extends back to August 2018. Since then, support for impeaching or impeaching and removing Trump has ranged over only about a 12-point spread in its polling average. That’s a spread similar to what Trump’s approval rating has been over the course of his presidency — and it’s a consistency that is also generally reminiscent of Trump’s approval.

Here’s how the two compare, adding in RealClearPolitics’ average of approval polling.