President Trump and his supporters have tried out a variety of talking points defending his attempts to press the Ukrainian government to open investigations that would benefit him politically.

As the public phase of the House’s impeachment inquiry begins on Wednesday, here are some of the most common rationales Republicans are putting forward to argue Mr. Trump’s actions are not impeachable, and how they stack up against the facts.

Attacking the whistle-blower and witnesses

Mr. Trump himself is the most vocal proponent of this shoot-the-messenger defense.

He has falsely claimed at least two dozen times that the whistle-blower complaint that spurred the impeachment inquiry was “inaccurate,” “false” or “a lie.” In fact, the White House released a reconstructed transcript of the president’s phone call with President Volodymyr Zelensky of Ukraine that corroborated much of what the whistle-blower reported. Witness testimony has also backed up and fleshed out the whistle-blower’s main points.

Mr. Trump has also accused Mark Zaid, a lawyer for the whistle-blower, of planning to “overthrow” the president, pointing to a 2017 Twitter post as proof. In the tweet, Mr. Zaid said a “coup” had started and impeachment would follow, in reaction to Mr. Trump firing Sally Q. Yates as acting attorney general. (Mr. Zaid told The Times last week that his tweet was taken out of context and that he had also represented the Republican National Committee.)