President Biden’s defenders have a new mantra: House Republicans are launching an impeachment inquiry “without evidence.” What a reversal from the Democratic precedent of using the process to uncover proof of wrongdoing by President Trump.

On Wednesday, the House of Representatives, based on allegations alone, voted along party lines to approve the inquiry into whether Mr. Biden gained from his son Hunter’s business dealings with foreign entities. The House included those in Russia and Communist China.

Hunter refused a House subpoena to testify in the matter. Had he appeared, he could have exercised his Fifth Amendment right against self-incrimination. In the new congressional paradigm, though, such a refusal is now cited as evidence itself, as is whistleblower testimony.

In a March 2023 tweet, Speaker Pelosi took the erosion of legal protections a step further. “Everyone has the right to a trial to prove innocence,” she said of Mr. Trump. In the Sun, I likened this reversal of “innocent until proven guilty” to the trial in Lewis Carroll’s, “Alice’s Adventures in Wonderland.”

In Carroll’s farce, Alice goes down the rabbit hole and runs afoul of Wonderland’s laws. The King of Hearts orders the jury to “consider their verdict” as soon as the White Rabbit, acting as defense counsel, finishes outlining the charges and before any evidence is presented.

The Queen of Hearts then issues her infamous decree, “Sentence first, verdict afterwards.” The remark has come to encapsulate upside-down trials, where anger and bias warp the justice system to reach a predetermined end.

In July,  Senator Paul warned against impeachment becoming this kind of routine investigative tool. “Let’s have quite a bit of evidence out there that the American people are actually behind this,” he said, “because I don’t really want to impeach every president.”

As I wrote in the Sun, Speaker McCarthy “told reporters that ‘to get to the bottom of the truth,’ the ‘only’ option is an impeachment inquiry which ‘gives us the apex of the power of Congress for Republicans and Democrats to gather the information that they need.’”

Mr. McCarthy stopped short of a formal inquiry. Now, as when Democrats launched their first impeachment inquiry against Mr. Trump, Republicans have leapt into the breach while speaking in solemn terms of the process.

“We do not take this responsibility lightly,” Speaker Johnson said in a statement after Wednesday’s vote, “and will not prejudge the investigation’s outcome, but the evidentiary record is impossible to ignore.” Republicans, again like Democrats, note that the inquiry is short of an actual impeachment vote.

In September 2019, the shoe was on Speaker Pelosi’s foot when she directed the chairmen of the six House committees investigating Mr. Trump to combine their efforts and “proceed under that umbrella of impeachment inquiry.”

A Democrat from Georgia, John Lewis, summarized why he backed using an impeachment inquiry to search for evidence. “I have been patient,” he said on the House floor, “while we tried every other path and used every other tool. We will never find the truth unless we … begin an official investigation as dictated by the Constitution.”

A Democrat of California, Adam Schiff, then chairman of the Intelligence Committee, said he resorted to that inquiry because the Trump Administration had refused to share information with the House. The situation was analogous to Hunter Biden, who may now be held in contempt of Congress.

The Democratic justification in 2019, borrowed from Watergate, was that Mr. Trump was “stonewalling.” As with the inquiry into President Nixon, however, there were issues of separation of powers and presidential privilege to be litigated before the White House had to open its books.

Whether evidence of high crimes and misdemeanors by Mr. Biden exists and is uncovered, impeachment is now closer to becoming the routine process that Dr. Paul saw on the horizon and warned against in July.

Expect Mr. Biden’s partisans to sound a lot like Republicans who defended President Trump’s as the inquiry unfolds. Amid their indignation, though, Democrats might pause to recall the part they played in sending us down this rabbit hole where a constitutional last resort is now business as usual.