What a difference Ukraine makes.

For months, Republicans gloated as Democrats agonized and squabbled over the question of impeaching President Trump. Should they? Dare they? Did the congressional investigations already taking place qualify as an impeachment inquiry? Grappling with a decision so monumental, and politically risky, the Democratic Party threatened to tear itself apart.

Then came last week’s announcement by Speaker Nancy Pelosi that a formal impeachment investigation was moving forward in the House. Faster than you can say “whistle-blower,” the dynamic flipped. Democrats united behind the message that Mr. Trump, in soliciting a foreign government’s help to undermine one of his domestic political rivals, had left them no choice but to pursue such an inquiry. Republicans struggled to respond, with some of their arguments more creative — and coherent — than others. Among their efforts:

Senator Lindsey Graham opted for a hard brushback: “To impeach any president over a phone call like this would be insane,” he told CNN last Wednesday, referring to the July 25 conversation between Mr. Trump and the Ukrainian president, Volodymyr Zelensky. “There is no there there,” he insisted on Fox News hours later, warning that “if this is an impeachable offense — this phone call — God help the next person to be president of the United States.”

The House minority leader, Kevin McCarthy, tried a gentler version of this on CBS’s “60 Minutes,” saying he interpreted the call as “two leaders having admiration, not intimidation.”

Mike Pompeo, the secretary of state, turned the tables, accusing House Democrats of trying to “intimidate, bully and treat improperly” five State Department officials called to give depositions starting this week on the Ukraine affair.