“What’s the real reason he didn’t run?” I asked Twitter today when I saw the news. “Not anti-semitic enough,” came the reply.

Really, though, I’m surprised. All signs seemed to point to him running. Others are surprised too:

Don’t forget (5) that he’s apparently the last remaining Democrat capable of winning a statewide seat in Ohio. Dems would loooooove to put that state back in play in 2020. Brown might be the only pol in the country capable of doing it. Alas for them, it’s not to be:

Brown, 66, said he made the decision Wednesday, a few days after he concluded a “Dignity of Work” tour of the first four caucus and primary states. The tour was intended to advance Brown’s labor-friendly populism while planting seeds for a national campaign…

A progressive fixture of the labor movement with one of the most reliably liberal voting records in Congress, Brown used his tour to position himself slightly more toward the center than some of the other Democratic hopefuls. A past proponent of single-payer health care, he did not embrace Medicare for All, instead favoring a more incremental approach: Medicare at 50. He also resisted calls to endorse the Green New Deal environmental agenda, dismissing it as sloganeering while still calling climate change “the greatest moral issue” facing Americans…

Brown also is an older white man who would have joined a race where diversity could be a selling point for candidates eager to run against President Donald Trump. Two of the other three Democrats to pass on the race this week — Sen. Jeff Merkley and former New York mayor Michael Bloomberg — are also older white men.

He was already out on the trail, he was pandering a bit to centrist voters by staying away from far-left proposals — what happened? Some on social media were speculating about possible #MeToo problems, but I doubt that’s it. Allegations that Brown shoved his first wife have followed him for years since the couple’s divorce, but he keeps winning elections and his ex is now a supporter of his. Brown surely anticipated that the issue would be raised at some point when he began thinking of running for president, yet he set a proto-campaign in motion anyway. Unless someone sprung some new dirt on him very recently, it doesn’t add up that that’s what dissuaded him.

The probable answer is more prosaic: Brown’s candidacy was always going to be conditional on what other potential candidates decided to do. He’s a blue-collar populist with possible special appeal to the Rust Belt as a midwestern guy himself. If Bernie had decided to pass on the race, Brown might have hung in there and tried to compete with Elizabeth Warren for the Sanders voters, a bloc big enough to have given Clinton a scare three years ago. But now that Bernie’s in, Brown’s in the same position as Warren is — a respected but pale-ish imitation of the class-warrior hero whom progressives most admire. Actually, Brown’s worse off than Warren since her name recognition is higher than his; he would have had a tough time gaining attention in a field with many bigger names. The BuzzFeed story I quoted above mentions a joint appearance with Cory Booker in South Carolina not long ago, with Booker drawing a much bigger crowd of admirers afterward.

With Bernie in, Brown’s candidacy maybe could have been refashioned into some sort of “only I can win the midwest” message, but (a) that’s a pretty niche segment of the electorate, however important, (b) the core promise of Sanders’s campaign is that he too can compete with Trump for the working-class white voters whom Hillary lost in the midwest (Sanders won the Michigan and Wisconsin primaries in 2016), and (c) with Biden looking increasingly likely to run, Brown wouldn’t even have the “midwestern white guy” lane to himself. He would have been a strong potential compromise candidate for Democratic voters had Sanders and Biden both passed on the race and a formidable populist alternative to Biden if only Bernie had passed. But with Sanders and Biden both in, why would Brown bother?

Some members of the chatterati think that he’ll concentrate on running for vice president now. Eh, not really. The Dem ticket will likely require racial and gender diversity; unless Kamala Harris is the nominee, Brown’s probably a nonstarter. And as much as Dems would like to put Ohio back in play, the state wasn’t close in 2016. It’s probably in the bag for Trump even if Brown is on the ticket unless he loses the national election so badly that Ohio won’t matter anyway. Brown’s endorsement should be coveted, though, especially by candidates like Biden and Warren who are eager to counter Bernie’s populist cred. Getting his seal of approval over Sanders might help in the midwestern primaries.