[guest post by Dana]
The timing of the announcement is a little bit on the nose, but overall it’s unsurprising news. From his op-ed:
Modern politics is trapped in a partisan death spiral, but there is an escape.
Most Americans are not rigidly partisan and do not feel well represented by either of the two major parties. In fact, the parties have become more partisan in part because they are catering to fewer people, as Americans are rejecting party affiliation in record numbers.
These same independent-minded Americans, however, tend to be less politically engaged than Red Team and Blue Team activists. Many avoid politics to focus on their own lives, while others don’t want to get into the muck with the radical partisans.
But we owe it to future generations to stand up for our constitutional republic so that Americans may continue to live free for centuries to come. Preserving liberty means telling the Republican Party and the Democratic Party that we’ll no longer let them play their partisan game at our expense.
Today, I am declaring my independence and leaving the Republican Party. No matter your circumstance, I’m asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us. I’m asking you to believe that we can do better than this two-party system — and to work toward it. If we continue to take America for granted, we will lose it.
President Trump took time out of his parade preparations to respond to the news, and gave credence to the “partisan death spiral” theory:

At least one GOP leader has already called for Amash to be stripped of his committee seat. Currently Amash holds a seat on the House Government Reform and Oversight Committee, as well as subcommittees for civil rights and national security:

Exit question: Does Amash run for president in 2020?
(Cross-posted at The Jury Talks Back.)
–Dana
UPDATE BY PATTERICO: Good for Amash. He’s about three years late to the party (pun intended), but it can’t be easy for an elected GOP congressman to leave his party, so I’ll cut him some slack. So: welcome to the #ExGOP club, congressman! We have pie!
If he runs, I’ll give him even more money, and will vote for him. I might even volunteer for the first time ever.
Yes, I know. He won’t win. It doesn’t change what I would do.