It is now a given. Donald J. Trump will conduct a mean, unorthodox and vile campaign for re-election as president of the United States.

The question facing Democrats as they look over their still quite large field of presidential candidates is: Who among them is willing and able to stand up to the onslaught that Trump will hurl at them?

I have my doubts about all of ’em.

I believe it is becoming clearer by the week, if not daily, that this campaign is going to rest between Trump and one of four, maybe five, Democratic contenders.

Joe Biden, Elizabeth Warren, Bernie (gulp!) Sanders, Pete Buttigieg and (maybe) Beto O’Rourke stand at the top of candidates who I think will stay the course beyond the first caucuses and primaries. If only Kamala Harris could shake the race up just a bit more.

It might be that someone will emerge as the gut fighter the Democrats will need if they have a chance of defeating the carnival barker in chief. Remember when former first lady Michelle Obama implored Democrats to “go high” when Republicans “go low”? We can kiss that mantra good bye, or so it appears to me at this moment.

Trump is a street fighter. The hideousness he displayed while beating Hillary Clinton in 2016 might resemble a hen party by the time he gets ramped up against whomever the Democratic Party nominates next summer to run against him.

I will lay this out right now, as if it’s a big surprise … which it isn’t. Any of the Democrats now in the field — with the possible exception of Bernie Sanders — would have my vote against Trump in November 2020. Why not possibly Bernie? Because his mantra about wealth inequality is becoming like a one-note samba.

Donald Trump never should have gotten elected in 2016. The Democrats’ major error was in nominating someone who had at least as many negatives going for her as Trump. I know what you might be thinking: Sure, you can say that now, even though you were predicting a big win for Hillary the last time. Well, I wasn’t alone.

I guess the task now for the field of Democratic challengers is for someone among them to emerge as the toughest of the bunch to handle the nastiness that is sure to come from the president.

I just wish someone could stake that claim.