The first round of polling data after the start of House Democrats' impeachment inquiry and details emerged of Donald Trump's phone call with Ukraine's president shows Americans are split on impeachment, but opinions may be shifting.

This week, Speaker of the House Nancy Pelosi, D-Calif., announced a formal impeachment probe, the Trump administration released a summary of the controversial phone call; and the whistleblower's complaint was declassified.

Impeachment:Trump impeachment inquiry begins with intel chief Joseph Maguire testimony

The call:'I would like you to do us a favor.' What Trump and Zelensky said in their July 25 phone call

The complaint:Read the full declassified text of the Trump whistleblower complaint

An NPR/PBS/Marist poll this week showed that 49% of respondents approve of the impeachment inquiry, while 46% do not approve.

That survey was conducted on Wednesday, the day the White House released the call summary and the day after the impeachment inquiry was announced, but before the whistleblower complaint was released.

Lee Miringoff, director of the Marist Institute for Public Opinion, noted that the next several days would be crucial as both Democrats and Republicans try to convince the American people of their respective beliefs around impeachment, according to NPR.

A second survey, conducted by Politico in partnership with Morning Consult, was done between Tuesday night and early Thursday — after the impeachment announcement but mostly before the whistleblower complaint was available to the public.

Of its respondents, an equal number (43%) said an impeachment inquiry should be launched as said it shouldn't.

Previous polling data showed most Americans didn't think impeachment was the right call. A Quinnipiac survey released this week and conducted Sept. 19-23 showed 37% of respondents thought the president should be impeached and removed from office.

That poll was conducted after news broke that a whistleblower complaint had been filed, but before the impeachment inquiry had begun.

Variances in data may be due, at least in part, to the way questions are phrased in these surveys. Quinnipiac asked respondents whether they thought Trump should be impeached and removed from office.

NPR/PBS/Marist asked whether respondents support the start of the official impeachment inquiry.

Politico/Morning Consult asked if Congress should begin impeachment proceedings and noting that as the first step in removal from office.

Timeline:A diagram of events in the impeachment inquiry of President Trump