Michael Bloomberg has delivered his latest delicious hint about running for president. Former Attorney General Eric Holder is fresh from taking credit for the new Democratic legislative majorities in Virginia, making it known he might be interested. And former Gov. Deval Patrick joined the presidential race after reportedly discerning a demand for another presidential candidate from Massachusetts. At this point, it might be helpful to note some patterns in former Democratic presidential nomination contests that might help late entrants.

The first is that opinion sometimes flows very rapidly and sweeps everything in its path, like lava down a volcano, like mud after the collapse of a dam, like the tide ebbing in the Bay of Fundy.

One example goes back to 1984 when Democrat Walter Mondale won 49% in a field of (only!) eight candidates in the Iowa caucuses. A fine performance, but all the attention went to Gary Hart, who, with his "new Democrat ideas," ran second with 17%. Hart swept New Hampshire 37 to 28% and won states like Florida and Massachusetts. Only Mondale's appeal to blue-collar whites -- a splinter group among today's Democrats -- helped him recover in Michigan, Illinois and New York and win the nomination.

Opinion flowed even more inexorably 20 years later. Anti-Iraq War Vermont Gov. Howard Dean attracted huge crowds and led polls in 2003, and on primary eve, Des Moines, Iowa, was swarming with Deaniacs in characteristic orange knit caps. But opinion was flowing away from Dean to the long-lagging John Kerry, who beat Dean 38 to 32%. After that, opinion just kept flowing. Kerry lost Vermont, the Carolinas and Oklahoma and won the rest of the states.

Sometimes Democratic opinion doesn't move much. The same demographic divisions prevailed in the close 2008 and 2016 races. In 2008, Hillary Clinton got enough support from "beer Democrats" to lead Barack Obama in votes and primary delegates, but his support from blacks and "wine Democrats" got him enough caucus wins and superdelegates for the nomination.

In 2016, Clinton lost beer Democrats to Sen. Bernie Sanders but won big-enough majorities from blacks, Hispanics and wine Democrats to win the nomination. This year, the holds of any candidate on these groups seem weak enough that a late enterer might hope that opinion will flow like lava to them.

Moreover, and this is my second point, wine Democrats may be numerous enough now to be analyzed as two demographic segments. Sen. Elizabeth Warren's and Bernie Sanders' big-government promises have attracted many white college graduates. But polling suggests they are "jug wine" folks, teachers and social workers with grad school degrees entitling them to public-employee union wage increases, and millennial 30-somethings still hoping to find themselves.

That may leave "champagne Democrats" up for grabs. In 2016, Sanders got more votes than Clinton from whites, but she handily carried the communities with the highest income -- Manhattan; Greenwich, Connecticut; New Trier Township in suburban Chicago; Lincoln and Lexington, Massachusetts; and Grosse Pointe and Bloomfield Hills, Michigan. Sanders' bland approval of 70% tax rates probably hurt him, and Warren's wealth tax may hurt her more, an obvious possible opening for a newcomer.

The third opening for late entrants could be black voters. Current polling shows Joe Biden, former President Barack Obama's vice president, leading among blacks. But Eric Holder, self-described as Obama's "wingman," has claims for that credential. He and Deval Patrick might enthuse the many black voters Sens. Cory Booker and Kamala Harris have failed to stir.

More important perhaps is the fact that black voters, with their above-average religious ties, currently say they're "less liberal" than most white Democrats on many cultural issues including supposed racial issues. As Columbia undergraduate (and rap performer) Coleman Hughes and New York Times writer (and veteran political reporter) Thomas Edsall both report, younger blacks are more concerned about creating jobs than climate change and believe that individual behavior is holding many blacks back more than societal racism. Reparations are not their thing, and they're the demographic group least supportive of same-sex marriage and trans rights.

Traditionally, blacks have voted almost unanimously for one candidate, a rational strategy for voters who see themselves as part of a group subject to systematic discrimination and disrespect. But there's evidence -- Bernie Sanders' holding Hillary Clinton to 68% of black votes in Michigan in 2016 and recent polls showing young black men significantly less Democratic than their elders -- that suggests such unanimity may be outmoded as blacks' incomes surge upward and overt discrimination becomes less and less common.

So a late-starting presidential campaign may not be hopeless, maybe not even for Hillary Clinton.