Interesting. I disagree. Their argument is that impeachment was taken seriously up to the Trump administration and is being trivialized by Republicans since. This sentence makes it clear that they think Trump's impeachments were serious:

Mr. Trump’s two acquittals made clear that a president could feel assured of keeping his office no matter how serious his transgressions, as long as his party stuck with him, and the impeachment-in-search-of-a-high-crime efforts of the Biden era have been written off as just more politics.

He's saying that impeachment should have worked but didn't because of Republicans. As opposed to Republican attempts to impeach Democrats:

Indeed, to the contrary, several Republicans have derided their party’s zeal for impeachment. Whatever his son Hunter did, they note, there is no evidence that Mr. Biden did anything wrong, and the Mayorkas impeachment centers on a policy dispute, not a criminal accusation.

And:

Michael J. Gerhardt, an impeachment scholar at the University of North Carolina, said Republicans were using impeachment not for accountability but for political damage. The pushes to impeach President Biden and Secretary Mayorkas are plainly attempts to make impeachment just another weapon in the partisan warfare of Washington,” he said.

And:

Indeed, it is that sting that may be driving Mr. Trump, who has made no secret of his desire to impeach Mr. Biden and his team as revenge for his own impeachments. “They did it to me,” he said in a radio interview last fall. “Had they not done it to me,” he added, “perhaps you wouldn’t have it being done to them.”

'Serious transgressions' vs 'no evidence of wrongdoing', 'partisan warfare', and 'revenge'.

It seems clear to me that, like we do, the author sees a fundamental difference between Democrats and Republicans. The Republican accusations are actually so frivolous that even the Biden administration themselves aren't concerned about them.

If anything, I think he's being too generous to the Republicans that impeached Clinton. I'd argue this is an acceleration of bad faith political theatre that began with Gingrich. It's something that's much worse now but not entirely new since Trump.

It gets decided in the senate? Impeachment is an inherently political process, but it is technically a conviction. (With a jury composed of the senate).

They can then impose further punishments in accordance with their sentence. Removal and future ineligibility are just the two most common.

Because its a political process, it is about convincing voters that it is valid. We'll see how these impeachments affect voters in the next election, and the ones to come. My understanding is that with Bill Clinton's impeachment, which R's believed was valid, but other wouldn't, led to Democrats winning seats in the house. Republicans were rather certain it did a lot of damage and would lead to them gain more seats in congress. Similar thing has happened with Trump, he even essentially lost his reelection due to some help of his impeachments. If republicans make a shitty show of their impeachment, people may see through it and still vote for biden.