I didn’t expect Donald Trump to win in 2016, and after his election I wrote an entire column in The Washington Post examining my analysis and mistakes. Now older, hopefully a little wiser, and definitely more cautious, I turn to the 2020 presidential contest, which has already started.

My initial rating is based on a combination of Trump’s current standing, his electoral performance in 2016, his party’s performance in 2018, questions about the Democratic Party’s ability to unite behind a broadly appealing nominee next year, and assumptions about the economy and state of the nation a year and a half from now.

Obviously, some of those factors will change over the next 22 months, altering the two parties’ prospects at least a few times between now and Nov. 3, 2020. But you have to start somewhere.

Watch: 2018 in 5 minutes — the best of congressional Hits and Misses

The fundamentals

Trump lost the popular vote by about 2.9 million votes (just over 2 percentage points), but won the White House by carrying states and districts that accounted for 306 electoral votes to Hillary Clinton’s 232.

Narrow wins in three key Great Lakes states that often go Democratic in presidential contests — Pennsylvania (20 electoral votes), Wisconsin (10) and Michigan (16) — were crucial for him, as were Florida (29), Arizona (11) and North Carolina (15), which he also won narrowly. Clinton fell 38 electoral votes short of winning the election.

Democrats showed renewed strength last year in Pennsylvania, Wisconsin and Michigan (including winning races for governor in all three), which complicates Trump’s re-election effort.

Of course, Trump narrowly lost four states he could conceivably carry in 2020 — New Hampshire (4), Minnesota (10), Nevada (6) and Maine (4), giving him at least a couple of paths to 270 electoral votes next year. (He did receive one of Maine’s four votes in 2016 when he carried the state’s 2nd District.)

Most other states don’t start off being in play in 2020, although a handful (e.g., Colorado, Iowa, Virginia and even Georgia) could be worth watching, if only to understand the dynamics of the larger fight.

In terms of his coalition, the good news for Trump is that he has suffered relatively few defections since his election. He remains strong in rural America, among evangelicals, with non-college-educated white men and with conservatives.

But the president has made no effort to broaden his appeal, a reality very much in evidence in 2018 survey data and in the midterm results.

How little has Trump’s coalition changed? He won 46.1 percent of the vote in the 2016 presidential contest. Two years later, his job approval in the exit poll stood at 45 percent, and Republican House nominees drew 44.8 percent of the vote in midterm balloting, according to data gathered by David Wasserman of the Cook Political Report.

Given the results of 2016 and 2018 (when Democratic House candidates drew almost 10 million votes more than GOP nominees), Trump again looks unlikely to win the popular vote next year.

In that case, the president’s re-election map probably will need to resemble 2016’s if he is going to win a second term.

The midterms showed that core Democratic constituencies that didn’t vote for Clinton in 2016, including younger voters, minorities and progressives, were back onboard against Trump.

In addition, white college-educated women (particularly in the suburbs) moved toward the Democrats last year.

If both of those developments occur again, the president will have huge problems, which is why Trump’s single-minded focus on his base over the past two years looks like a strategic error.

The polls

While initial 2020 polls should be taken with a pound of salt, they illuminate the president’s vulnerabilities. The Dec. 9-12 NBC News/Wall Street Journal poll showed Trump trailing a “generic Democrat” by 14 points, 52 percent to 38 percent.

Of course, without a specific Democrat named in the hypothetical ballot test, the matchup is more of a referendum on Trump than the choice of nominees that 2020 will be.

The “generic ballot” test therefore may well exaggerate the president’s weakness, since the eventual Democratic nominee is likely to have liabilities that don’t show up in any generic ballot.

In addition, Democrats will have a potentially nasty primary fight in 2020, which could easily produce a flawed nominee who, like Clinton, cannot unite anti-Trump voters.

And the eventual Democratic nominee may have to tack so far left to win the nomination that swing voters will not be comfortable supporting a progressive who calls for higher taxes and Medicare for all (single-payer health care).

It’s wise to be cautious about early polls, since the president’s numbers surely will bounce around over the next year and a half.

But his mediocre job approval ratings and weak early standing in ballot tests are troubling for GOP strategists.

Events

There is no way of knowing what events will draw America’s attention 18 or 20 months from now, but Republicans have reasons for concern.

Trump clearly likes to keep himself in the middle of things, and that inevitably leads to disruption and chaos. That’s not a problem for most of his base, of course, but it could make the Democratic nominee more appealing to some voters who supported Trump in 2016 but have tired of the circus.

The economy, which has been strong during the first two years of the Trump presidency, looks increasingly vulnerable to higher interest rates, slower international growth and the normal ups and downs of the business cycle.

Most economists expect slowing growth in the U.S. economy by later this year and in early 2020, and while that doesn’t necessarily mean a recession, even slower growth could cause additional headaches for the president’s campaign.

Administration turnover, Trump’s leadership style, and questions involving trade/tariffs, China, Russia, NATO, the Middle East, the budget deficit, health care, immigration, gun control and defense could all be issues over the next couple of years, keeping the president on the defensive.

And that doesn’t even include additional Trump problems stemming from the special counsel investigation by Robert S. Mueller III and House investigations into his business dealings and administration’s performance.

Of course, House Democrats could overplay their hand, giving Trump more and better options than he has now and making themselves an issue rather than keeping the focus on the president and his administration.

But so far, the Democratic leadership seems to understand the risks to impeachment.

The bottom line

Both parties face significant challenges. The president has alienated too many voters for his own good, limiting his appeal and forcing him to negotiate a narrow path toward a re-election that looks more difficult after Democratic victories in the midterms.

Democrats, on the other hand, face turnout and persuasion challenges as they seek a nominee who can both rally the party’s base and appeal to swing voters, some of whom find the party’s progressive agenda no more palatable than Trump’s performance in office.

The president is not the political basket case that some portray him.

Barack Obama won a second term even after a disastrous first midterm election, and Trump’s base remains largely intact.

Moreover, the electoral college narrowly favors the GOP.

Given all of these considerations, 2020 starts off as a competitive contest, though not a pure toss-up.

There are too many questions surrounding the president’s re-election prospects to call the race even, and there are too many opportunities for the Democrats to blunder toward a weak general election nominee to rate the race Leans Democratic.

So, given the upset in 2016 and the uncertainties of the next year and a half, I would start rating the 2020 contest broadly as a toss-up/tilting Democratic. And, once again, fewer than a dozen states likely will pick the next president.