It's very hard to see how Donald Trump isn't the Republican nominee in 2020

Relive election night 2016
Relive election night 2016


    Relive election night 2016


Relive election night 2016 02:37

(CNN)There's a remarkably persistent idea in Washington circles that President Donald Trump is likely to face a serious challenge for the Republican nomination in 2020. Whether it's Ohio Gov. John Kasich or Arizona Sen. Jeff Flake or someone else, Trump is going to have a fight on his hands to be the GOP nominee in two years' time, the argument goes.

The problem with that line of thinking is that there is, roughly, zero evidence that it is true. And there's lots and lots of evidence the opposite -- that Trump will coast to his party's nomination in 2020 -- is, in fact, correct.
Take Tuesday night.
    Trump critic Mark Sanford loses a primary because he, occasionally, had the temerity to question Trump's views publicly. Corey Stewart, Trump's former Virginia state director in 2016, wins the Old Dominion Senate nomination running on his support for Trump and for keeping Confederate statues up.
    Those are only the most recent examples. For all the lauding of Flake -- who wrote a book in 2017 crushing Trump and the Republican Party that supported him -- the simple fact is that Flake's anti-Trump views led to a precipitous drop in his polling. Flake left the race because his chances of winning renomination were somewhere between "slim" and "none." (Flake was opposed by two candidates -- Kelli Ward and Joe Arpaio -- who were actively linking themselves to Trump and his policies.)
    Then there's Kasich. Recall that Kasich actually ran for president in 2016. Against Trump. And he went nowhere. Trump won 1,447 delegates in that race, compared to 161 for Kasich. And it's not as though Republican voters didn't know what they were getting in Trump. Say what you will about him, Trump made no attempt to disguise his views (or lack thereof) during the primary fight.
    As CNN's Harry Enten noted recently, Trump is inarguably in a stronger place today with rank-and-file Republicans than he was back then. Writes Harry:
    "The problem that Trump's Republican adversaries are learning is that it's not 2016 anymore. Even as Trump was winning the presidential election, his net favorability (favorable-unfavorable) rating among Republicans in an average of polls was just +50 points. That's far short of the maximum +100 point rating. You could, in other words, oppose or critique Trump as a Republican (as Sanford did in 2016) and not get chased out of the party.
    "Today, it's totally different. Trump's net favorability among Republicans is up to +71 percentage points on average. There are very few Republicans who disagree with Trump. Trump's approval rating (a slightly different measure than favorable rating) stands at 87% in the latest Gallup poll. To put that in perspective, only two other presidents since 1950 have had higher approval ratings among their own party heading into a potential presidential primary."
    There is simply no path for Kasich or Flake or, at the moment, anyone else around Trump's coalition.
    There was a time -- back around 2008 -- when you could conceptualize a Republican presidential race in three basic lanes:
    1. Establishment lane
    2. Social conservative lane
    3. Moderate/liberal lane
    The 2016 campaign destroyed that way of thinking about the Republican Party. That race produced only two lanes:
    1. Trump
    2. Not Trump
    In the context of the 2016 election, there was a real opening to be the "Not Trump" candidate. The problem was that all of the candidates not named "Donald Trump" were still operating on the three-lane way of thinking. They thought Trump was a joke or, if he wasn't a joke, he was a phenomenon that would flicker out long before voters actually began voting.
    By the time they realized there was only two lanes in the party -- and that 15 of them were in one lane and one (Trump) was in the other -- it was way too late.
    Now that Trump is President, the two lanes still exist. But the mistake the adherents to the "he's going to be in a battle for the 2020 nomination!" idea make is to assume those two lanes are of roughly equivalent size. They are not. One is a superhighway. The other is a dirt road. (If you aren't sure which is which, scroll back up and try again. Or check to make sure you are currently awake.)
    Could this change? OF COURSE!
    The most obvious change agent is special counsel Robert Mueller and his ongoing probe into Russian interference in the 2016 election as well as the possibility of collusion and obstruction. If Mueller's final report provides incontrovertible evidence of wrongdoing by Trump -- and we have no evidence that is or will be the case -- then the calculations outlined above change.
    Or if Trump suddenly pivots and abandons his pledge to build a border wall. Or makes a series of major concessions on trade with Mexico and Canada. (Of course, if that happens, the primary challenger with a real chance would come from Trump's ideological right -- not his left, which is where the likes of Flake and Kasich are positioned.)
    But all of those scenarios are not only big "ifs," but also seem very, very unlikely. If the next 16 months proceed like the first 16 months of Trump's presidency have, there's almost no chance Trump has anything more than a nominal primary challenge. The numbers just aren't there.