With considerable fanfare, billionaire philanthropist Tom Steyer has announced a $10 million national advertising campaign aimed at impeaching Donald Trump.

Speaking in one of his own ads, Steyer says that “people in Congress and his own administration know that this president is a clear and present danger who is mentally unstable and armed with nuclear weapons.’’ More than 1 million citizens are said to have signed Steyer’s petition urging Congress to impeach Trump.

Steyer is a reliable contrary indicator where political betting is concerned. The conservative Washington Times cruelly called him “the Biggest Loser’’ in the 2016 election cycle, noting that he had spent $88 million to back four losers, including Hillary Clinton, in federal elections.

That outcome was a replay of the 2014 elections, when Politico reported that Steyer’s Climate Action Committee threw $65 million at state and local races, only to see “the vast majority of their favored candidates in the battleground states go down to defeat.’’

Steyer and his riches love to be parted. Democrats have been talking about impeaching Trump since even before he took office, which seems a bit hasty to me. Now everybody is putting their oars in: Several California towns, plus the Los Angeles City Council; plus Brookline, the no-spanking capital of Massachusetts; and of course Amherst, “the kind of place that has a fine public school system and a foreign policy,’’ according to Tracy Kidder, in his 1985 book “House.’’

I wonder if impeachment dreamers really understand what needs to happen in order for Trump to get the heave-ho. First, Democrats would have to win a majority in the House of Representatives in 2018, a possibility but far from a sure thing. Second, as we saw with Bill Clinton, you can be impeached and stay in office. The Republican — repeat, Republican — Senate came nowhere near ousting Bill Clinton in 1999.

Lastly, impeachment takes forever. The lawsuit that engendered the 1998 articles of impeachment against Clinton was filed in 1994. Clinton was impeached in late 1998, and the Senate failed to convict him in 1999. Who knows what might bring Trump down? I’d bet on his family’s rampant self-dealing, but perhaps the “Russia investigation,’’ which means different things to different people, may sink him.

Even if — and that’s a big if — viable charges stuck to Trump, his lawyers would certainly take several years to litigate them. That’s a lotta years of Trumpismo, to be sure.

Maybe Steyer likes his odds. It’s said that his impeachment stunt is really a back-door attack on senescent Senator Dianne Feinstein of California, whom Steyer may challenge next year. The famous London betting house Ladbrokes thinks Trump will serve out his first term (60 percent chance), but they are not very bullish on his reelection (30 per cent chance).

Here is a Ladbrokes classic of yesteryear: “Jeb Bush Now Favourite to be 2016 Republican Candidate.’’ They have been wrong before. So has Tom Steyer, and so have I.

Alex Beam’s column appears regularly in the Globe. Follow him on Twitter @imalexbeamyrnot.