Supporters listen to Democratic Senate candidate Beto O'Rourke, following his defeat to incumbent Ted Cruz, at a rally at Southwest University Park in El Paso on Nov. 6, 2018. (Michael Robinson Chavez/The Washington Post)
Opinion writer

President Trump takes solace from his high approval rating among Republicans. That, however, has come at the expense of support among women, the college-educated, nonwhites, independents, the young, etc. And that dichotomy will increasingly put him at risk for a simple reason: The GOP isn’t what it once was.

Gallup reports:

Significantly more U.S. adults continued to identify as political independents (42%) in 2018 than as either Democrats (30%) or Republicans (26%). At least four in 10 Americans have been political independents in seven of the past eight years, including a record-high 43% in 2014. ...

In just the past decade, an increasing proportion of adults have identified as independents, reaching 40% for the first time in 2011 and generally maintaining or exceeding that level since then. As a result, since 2011, the percentage of independents has exceeded the percentage identifying with the Democratic Party by 11 points on average, and the percentage identifying as Republicans by 14 points.

“Eighty percent of Republicans” may sound good, but if the GOP is only 26 percent of the electorate, that gives Trump just under 21 percent of the entire pie. That’s awful, to put it mildly.

Well, you say, independents aren’t truly independent; they tend to lean toward one party or the other. That’s accurate — and unhelpful for Republicans. (“47% of Americans on average in 2018 were Democratic identifiers or Democratic-leaning independents, and 41% were Republicans or Republican-leaning independents.”) Republicans win only when they can turn out a disproportionately high percentage of their side and/or Democrats fail to do the same. That’s the formula that allowed President Trump to win in 2016. Two years later, however, his pool of Republican voters has shrunk, and independents in poll after poll overwhelmingly disapprove of his performance. If Republicans run Trump or another candidate equally dependent on a shrinking share of the electorate, a good Democratic turnout is likely to produce a Democratic president. That’s what happened on a congressional level in 2018.

Democrats should keep in mind three things. First, not that Trump needs much encouragement, but baiting him into taking more and more extreme, base-pleasing positions certainly helps Democrats. The shutdown, for this very reason, should (and likely does) thrill Democrats. Take an unpopular position (the wall) and try to obtain it through unpopular means (a shutdown) while engaging in unpopular tweeting (even his GOP supporters would rather he lay off Twitter)? Democrats will respond, “Where do we sign up for that!?”

This leads to the second imperative for Democrats: Chase Trump to the fringe, but keep grounded with the electorate that delivered them huge wins in the 2018 midterms. That includes women, college-educated voters and suburbanites. No wonder House Speaker Nancy Pelosi wants to focus on health care, wages and reasonable gun-safety measures. Staying on those topics is a lot less risky than talking about impeachment, which turns off a majority of voters. When Trump is railing, Democrats should be reasonable and methodical. When Trump is tossing invectives, Democrats should fact-check him in real time. The Democrats' base, when the time comes, will crawl over broken glass to turn out in 2020; their bigger risk is in losing a flock of voters who gave them a chance in 2018.

Finally, Republicans’ available pool of voters — old, white men — is fixed, and indeed declining. The pool of Democrats' persuadable voters continues to grow. Democrats cannot afford to sit on their hands after successful outreach to irregular voters (Hispanics, young voters) in 2018. Registration and turnout of new voters are not one-election propositions. If Democrats aren’t spending the next two years doubling down on registration and engagement of such voters, they’re throwing away a big advantage.

In sum, the crazier Trump gets, the nuttier and smaller his base becomes. That’s good news for Democrats — provided they don’t copy his strategy on the left (chasing winnable independents away) or lose momentum in their registration efforts.