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As President Trump has been openly feuding with House Democrats pursuing investigations into him, his administration and his finances, more than 200 lawmakers -- almost entirely Democrats -- are calling to start an impeachment inquiry, the first step in a lengthy and likely divisive process.

There has been a surge in support of launching an inquiry amid a growing controversy over Trump's July 25 call with Ukrainian President Volodymyr Zelensky where he discussed former Vice President Joe Biden. On Tuesday, Speaker Nancy Pelosi announced a formal impeachment inquiry into the President, and the number of House Democrats who at least support launching an impeachment inquiry is quickly approaching the 218 votes needed to impeach Trump in the House, though it is unknown if all those who are in favor of an impeachment inquiry will vote to do so.

CNN previously reported that Trump pressed Zelensky to investigate Biden's son, Hunter, according to a person familiar with the situation, and that call was part of the whistleblower complaint submitted to the Intelligence Community Inspector General, another person familiar with the situation told CNN. Trump has admitted he delayed aid to Ukraine ahead of the call, but has denied doing anything improper.

There has been no evidence of wrongdoing by either Joe or Hunter Biden.

Many Democratic lawmakers had previously opened the door to impeachment proceedings after testimony from former special counsel Robert Mueller before Congress in July. More than four dozen House Democrats came out publicly in support of an impeachment inquiry following Mueller's appearance -- including House Foreign Affairs Chairman Eliot Engel of New York and House Judiciary Chairman Jerry Nadler.

Impeachment appears politically risky for Democrats for many reasons, not least of which is that even if the House could get a majority to support impeachment, it likely would go nowhere in the Republican-controlled Senate.

While there are varying degrees of how far critics of the President are willing to push the process, one relatively basic litmus test is whether lawmakers would support starting an impeachment inquiry, the first significant step in the process.