With Sen. Elizabeth Warren, D-Mass., entering the race for president by announcing she was starting an exploratory committee, a key aspect of the decision that Democrats will have to make about their nominee in 2020 is becoming more clear. 

Collectively, the Democrats have to choose whether they want a fighter who will take on President Donald Trump in a brawl or a candidate who is a more low-key anti-Trump persona. A fighter would try to embody and harness the outrage that excites the hardcore Trump resistance. The cooler anti-Trump candidate would present themselves as offering a plea for peace and a return to normalcy in America's politics.

If the Democrats nominate an aggressive, hot personality, they will be asking voters to choose between two well-defined candidates. If they pick a candidate who is stylistically the opposite of Trump and who can avoid direct engagement with the president, then the election will be about whether voters want more Trump or less Trump.

Warren is more of a fighter. She has been an outspoken critic of all things Trump. She and the president have famously fought about her Native American heritage or lack thereof. She is a more aggressive and more liberal politician than Hillary Clinton. And, in my opinion, Warren will energize the Democratic Party's core voters more than Clinton did in 2016. A candidate with a calmer demeanor and a more subtle approach may leave Democrats cool, lacking enthusiasm and suppressing their voter turnout.

That said, I am reminded of the 1994 New York governor's race, when George Pataki beat the three-term incumbent Mario Cuomo. Cuomo was wildly unpopular; Pataki was a little-known state senator. He was as anonymous as a candidate for governor could be. He never let himself become the issue, and he could never be characterized as an extremist. Pataki won because he was the person on the ballot who was not Cuomo.

So, in 2020, Democrats need to ask themselves if they will be better off having voters choose between two brawling candidates or if they want to try to let Trump beat himself. With Trump as unpopular as he is, it seems plausible that the Democrats' nominee could practically go into hiding immediately after the July 2020 convention and let Trump be Trump at his own peril. That may be their plan if the Democrats don't pick a hostile lightning rod of a candidate who Trump could bait and pull into the gutter.

A cooler anti-Trump candidate would be someone more like Sen. Amy Klobuchar, D-Minn., and less like Warren. Klobuchar has an earnestness about her and a calm demeanor that Warren lacks. Klobuchar represents a class of Democratic candidates that would be less confrontational and more able to stay out of the way, making the election a referendum on Trump.

So, are the Democrats in the mood for cool and composed, or are they determined to go hand-to-hand with Trump?

Ed Rogers is a veteran of the Ronald Reagan and George H.W. Bush White Houses and several national campaigns.