Why the Biden-Trump feud of 2018 might be a preview of 2020

(CNN)President Donald Trump and former Vice President Joe Biden are engaging in a war of words about beating each other up.

On Wednesday, Biden said that if he and Trump were in high school, he would "take him behind the gym and beat the hell out of him."
Trump responded on Thursday, tweeting, "Crazy Joe Biden is trying to act like a tough guy. Actually, he is weak, both mentally and physically, and yet he threatens me, for the second time, with physical assault. He doesn't know me, but he would go down fast and hard, crying all the way. Don't threaten people Joe!"
This all feels like a preview of a Biden and Trump face-off come 2020. And, in fact, Biden versus Trump is probably the highest probability matchup compared to all the others at this moment in time, though it's still a relative long-shot.
    Now, a word of caution: Early polls are early polls and who knows who might enter the presidential race. It's hard enough for polls to forecast a winner within a week of an election. It's entirely unreasonable to believe they can forecast a winner at this point.
    What the polls are good for is telling you who comes to Democratic voters' minds when thinking about who they believe is the leader or next leader of the party.
    And right now, that person is Biden.
    In an average of national polls taken this year, he's polling at 27% among a field of potential Democratic contenders in 2020. The only person close to him is Sen. Bernie Sanders who is at 21%. Sanders is earning far below the 43% he won in the 2016 primary. Biden, meanwhile, is earning far higher than 0.2% he took in 2008. No one else comes close to either candidate.
    Biden even leads in New Hampshire, which is right next to Sanders' home state of Vermont and where he crushed Clinton in the 2016 primary. A February University of New Hampshire survey put Biden at 35% to Sanders at 24%. Sen. Elizabeth Warren, from next-door Massachusetts, was the only other candidate polling in the double-digits.
    Biden, who has been running for president going back 30 years, is in the best position he has ever been at this point to claim the Democratic nomination for president.
    Before this go-round, very few Democrats thought of Biden as the leader at this point in the nascent primary campaign.
    Before Biden ran for president in the 1988 campaign, he started off in a deep hole. Less than 1% of Democrats selected him as their choice to be the Democratic nominee in a February 1986 ABC News/Washington Post poll for the 1988 Democratic nomination. This was good for dead last. Eventually, Biden's campaign would go down amid a plagiarism scandal.
    There were also talks of a Biden campaign in 2004. Again, few Democrats thought of Biden as the obvious next choice. He sat in ninth place at a little over 2% in an average of 2004 primary polls taken between January and March of 2002. Biden didn't end up running.
    Biden actually did pull the trigger on a 2008 campaign. He shot up to an average 4% in the early primary polls (January to March 2006) that cycle. Still, he was in a distant fifth place and would drop out after a poor showing at the Iowa Caucus.
    It was after this campaign that Biden arguably caught the break of a political lifetime. He became Barack Obama's running-mate and was elected to be vice-president. You would think that this would have made him the top choice for Democrats in 2016.
    But, Biden ran into the electoral bulldozer Hillary Clinton. The former secretary of state was polling in the 60s and 70s in early primary polls, the highest percentage ever for a non-incumbent. Biden's 12% did place him second, but clearly he wasn't the leader of the party. Biden would end up announcing in late 2015 that he was taking a pass on 2016.
    Now though, there is no Clinton for Biden to contend with. He is, after more than 30 years, the leader of the Democratic field. Biden has a straight shot at the Republican president. He's going around campaigning like he will run for president, and there's no real reason to doubt it's a strong possibility.
    With these facts in mind, my guess is that the tat we're seeing between Biden and Trump today is just the first of many to come.