Let’s consider the conundrum of the three Bs.

Bernie, Biden and Bloomberg.

Despite our great fondness for Iowa, its quadrennial caucuses are costly and fairly meaningless exercises. Since 1972, only three men won a contested Iowa caucus and went on to become president — Barack Obama, George W. Bush and Jimmy Carter. In 2016, Texas GOP Sen. Ted Cruz won Iowa and Donald Trump came in second.

So the odds are better than even that after all the Iowa hoopla, we won’t know much more about the upcoming presidential sweepstakes than we do now.

Vermont Sen. Bernie Sanders, with a huge ground game in Iowa left over from 2016, is exceedingly popular with young Democrats in the state. But it remains unlikely that he could sway enough moderate Democrats to get the party nomination.

The Trump campaign would like nothing better than running against a white-haired septuagenarian who has had a heart attack and declares he is a democratic socialist. Fox News prays “Go, Bernie, go!”

Former Vice President Joe Biden, not likely to win Iowa, still remains the favorite to get the party nomination. But he has been damaged — unfairly — by the scandal over Trump exhorting Ukraine to open a bogus investigation of him and his son Hunter.

There is no smoking gun there, but Trump has succeeded in convincing many Americans that somehow Biden is culpable of something even if they don’t know what. It’s wrong and unfair, but it’s exactly what Trump did to Hillary Clinton. Many still think Trump’s barrage of nasty criticism of her as corrupt means something was wrong even after it has been positively proven she was innocent of any wrongdoing (although guilty of running a bad campaign).

Former New York City Mayor Michael Bloomberg has changed his party affiliation from Republican to Democrat to run for president, but he is not even running in Iowa. Nonetheless, he has spent millions of dollars in TV ads trying to convince Americans that Trump is the worst president in U.S. history.

More to the point, he vows that he will spend $1 billion of his self-made $50 billion fortune to defeat Trump, no matter who is the Democratic nominee. Bloomberg is a centrist, and on many social issues he is in line with a majority of Democrats. But even many of the Democrats most fiercely passionate about dumping Trump scoff that they don’t want to facilitate a nominee who hopes to buy their nomination. And a lot of them are still angry about his stop-and-frisk policy when he was mayor.

The big question of 2020 is whether Trump has changed politics forever. Are nastiness, deliberate falsehoods and lack of civility now required? Do Americans now demand constant titillation from their politicians?

Bernie, Biden and Bloomberg are old school. They don’t really seem to have the stomach to fight dirty. If one of them winds up as the official counterpuncher to Trump, is Trump a shoo-in for reelection?

Could Bernie convince enough Americans that it’s time for an old-timey socialist? Could Biden convince enough Americans that he is not tainted by Trump’s false allegations about Ukraine? Could Bloomberg convince enough Americans that another New York City billionaire is worth taking a chance on?

The two other potentially realistic alternatives are two senior women senators — Minnesota Nice Amy Klobuchar and Massachusetts Liberal Elizabeth Warren. Is America finally ready to vote a woman into the White House? Is there a surprise coming? Both women can claim they never lost an election.

Let’s admit that while Trump was sucking all the air out of the room by getting himself impeached, a lot of us haven’t paid much attention to what was happening in Iowa. Let’s face it, the Democratic debates were not all that exciting.

But now we’re in a new chapter. Now it gets serious. Now we have to pay attention.

After Iowa, we’re still left with the quandary we started with — which candidate could defeat Trump in an all-out, no-holds-barred fight?

Ann McFeatters is an op-ed columnist for Tribune News Service.