Sen. Joe Manchin may have just killed off a big chunk of President Biden's agenda. The West Virginia Democrat has made it clear that he won't go along with his party's hopes to kill — or at least amend — the de facto supermajority requirement for most legislation that passes through the upper chamber of Congress.

"There is no circumstance in which I will vote to eliminate or weaken the filibuster," he writes in a new op-ed for The Washington Post. "The time has come to end these political games, and to usher a new era of bipartisanship where we find common ground on the major policy debates facing our nation."

Manchin's seemingly definitive declaration produced much weeping and gnashing of teeth on the left, and understandably so. Some big priorities for Democrats — such as HR 1, the voting rights bill now making its way through the legislative process — might well be impossible to pass in the near future: The party has just 50 votes at its disposal, along with the vice president's potential tie-breaker that technically gives it a majority in the Senate, but it won't get the 60 votes needed to break a certain Republican filibuster.

I've not been one to hold Manchin in contempt. In many ways, he is behaving rationally for an elected official who doesn't want to alienate Republican voters in his deep-red state. It is in his political interest to be seen as a Democrat who isn't quite as Democratic as the rest of his party. But his op-ed, which also takes a whack at the reconciliation process that occasionally allows budget-related bills to pass with a majority vote, makes an unconvincing case for keeping the filibuster.

Three bad ideas stand out and need addressing:

Weakening the filibuster has produced more gridlock in the Senate. "Every time the Senate voted to weaken the filibuster in the past decade, the political dysfunction and gridlock have grown more severe," Manchin writes, citing changes that let the Senate approve Cabinet nominees, federal judges, and Supreme Court justices on a simple majority vote.

That's clearly not true. In the year before Democrats used the "nuclear option" in 2013 to end the filibuster on most judicial appointments, the Senate was able to confirm just 36 federal judges appointed by then-President Barack Obama. The year after? Eighty-four new judges. And whatever you think of the decision by Sen. Mitch McConnell (R-Ky.) to nuke the filibuster for Supreme Court appointments in 2017, that decision allowed Republicans to confirm three new justices during President Donald Trump's term. Where the filibuster has been weakened, Senate productivity has followed.

Eliminating the filibuster would produce wild swings in governance. "If the filibuster is eliminated or budget reconciliation becomes the norm, a new and dangerous precedent will be set to pass sweeping, partisan legislation that changes the direction of our nation every time there is a change in political control," Manchin writes.

This notion ignores that even without the filibuster, turning bills into a law would still be a pretty cumbersome process. The bicameral nature of the legislative branch means Congress checks and balances itself without any outside help. Majorities in both the House and Senate must agree on the exact same language and priorities in order to get a bill passed, and even then a president must sign off before it becomes law. Such opportunities are rare: In the 21st century, Obama and Trump entered office with their respective parties in full control of the White House and Congress, then saw at least one chamber flip to the opposing party at the next midterm election.

Manchin also ignores very recent history on this front. The new $1.9 trillion COVID relief bill passed the Senate last month on a party-line vote using the reconciliation process — a piece of "sweeping partisan legislation" that happened only because there was a "change in political control" after the November election. Manchin voted for that bill.

Bipartisanship can be wished into existence. "Senate Democrats must avoid the temptation to abandon our Republican colleagues on important national issues," he writes. "Republicans, however, have a responsibility to stop saying no, and participate in finding real compromise with Democrats."

How does Manchin think this will happen? One big lesson of the last decade or so in American politics is that Republicans feel little responsibility to stop saying no, and see lots of reasons to obstruct Democratic governance. They believe, with good reason, that "saying no" is their path back to power. Manchin's furrowed brow won't change that.

Thanks to the reconciliation process, Democrats still have a couple of big swings they can take as long as they remain in control of the Senate. But Manchin's decision to foreclose any changes to the filibuster means the party will have to narrow the scope of its ambitions.