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One week ago, it was already clear that President Trump, among his many unconstitutional misdeeds, had pressured Ukraine to smear Joe Biden. And yet the chances that the House Democratic Caucus was going to impeach Trump looked minuscule.

Today, the chances look significantly better. So what changed?

For the first time in a long time, Trump committed an act of lawlessness so extreme that it created a news story that managed to feel both fresh and surprising: A whistle-blower came forward to file a complaint about Trump lobbying the president of Ukraine during a phone call. The inspector general for the nation’s spy agencies found the complaint credible enough that he tried to refer it to Congress. It now seems Trump was using American foreign aid to threaten the Ukrainian President.

Appearances matter in politics.

Yes, Robert Mueller’s report contained extensive evidence of impeachable wrongdoing by Trump. Yet it didn’t contain as much evidence as many people expected. And Mueller was sufficiently feckless in his presentation of the report that Trump’s attorney general was able to misrepresent it.