There were three big-time events over the weekend.

Tiger Woods pulled off the most remarkable comeback in any sport with his Masters win. (And Donald Trump called it, said he'd win majors after they played together in February, you've gotta give him that.)

Pete Buttigieg delivered an announcement speech (soon after the 18th hole) that drew Tiger levels of praise, as the media lovefest with the South Bend mayor continues unabated. (Beto who?)

And Bernie Sanders picked a fight with a liberal website, making sure it was leaked to The New York Times.

It's long past time to take Bernie seriously. "Bernie Sanders is the Democratic Front-Runner," says the Atlantic.

"Stop Thinking of Bernie Sanders As a Gadfly. He's the Front-Runner," cautions the L.A. Times.

He's raised the most money ($18 million), he's drawing big crowds, and in a new Emerson poll, he edges out the undeclared Joe Biden, 29 to 25 percent.

Sanders even forced himself to talk to reporters for the first time in two months on the trail.

So why on earth is he starting an intra-party battle with a scathing letter to the Center for American Progress?

In the letter, Sanders wrote: "This counterproductive negative campaigning needs to stop. The Democratic primary must be a campaign of ideas, not of bad-faith smears. Please help play a constructive role in the effort to defeat Donald Trump."

The backstory: The Center for American Progress is a Hillary-centric think tank, founded by John Podesta 16 years ago and funded in part by George Soros. It remains filled with Democratic establishment figures.

Sanders undoubtedly got screwed by the DNC and the party apparatus in 2016, when the playing field, including a meager number of debates, was tilted to favor Hillary Clinton. So he's understandably sensitive on the subject.

But Bernie's beef is with ThinkProgress, a liberal website that is affiliated with CAP but which both groups say is editorially independent.

What really burned Bernie was a posting that began: "It's all very off-brand and embarrassing, but Sen. Bernie Sanders is a millionaire. Turns out railing against 'millionaires and billionaires' can be quite the lucrative enterprise."

Now I happen to think this is utter BS. The Vermont senator achieved millionaire status in part by writing a book that became a best-seller. Absolutely nothing wrong with that. And Sanders made that point forcefully last night at a Fox News town hall with Bret Baier and Martha MacCallum.

Sanders accused ThinkProgress of "dishonesty" and said the site was also being unfair to fellow liberals Elizabeth Warren and Cory Booker.

ThinkProgress editor-in-chief Jodi Enda, a former CNN and Knight-Ridder reporter, responded by saying her site will not take sides in the Democratic primaries. "Political leaders should not be able to muzzle or stop coverage that they consider critical," said Enda's statement, reported by the Times.

But by yesterday CAP President Neera Tanden had backed down, saying a ThinkProgress video on Sanders “is overly harsh and does not reflect our approach to a constructive debate of the issues.”

Sanders is obviously trying to send a message. But isn't he punching down by going after an ideological website?

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In other words, if he's on track to win the Democratic presidential nomination, he should be brushing off criticism by liberal writers. The letter makes him sound hypersensitive — and the leak broadcast the dispute to many millions who would never have seen the ThinkProgress post.

Sanders is about to draw far tougher press scrutiny than he did in 2016, when the media never thought he had a shot at beating Hillary. And how he deals with that scrutiny will show people whether he has the toughness to take on Trump.