Strong Economies Lift Presidents. Trump Seems an Exception.

The stock market has surged. Unemployment is at 4.1 percent. ISIS has largely been vanquished from Iraq and Syria.

But despite it all, Donald J. Trump’s approval ratings are mired in the upper 30s. No president has had worse ratings at this stage of his term since modern polling began more than three-quarters of a century ago.

With President Trump starting the new year with a blizzard of tweets and fresh controversy seemingly every day, there are still debates about whether he is as weak as he looks. After all, he managed to win the presidency with terrible favorability ratings a little over a year ago. Analysts have understandably been cautious about assuming that his weak ratings will doom him or his party again.

But it seems clear that Mr. Trump’s approval ratings betray significant political weakness.

Setting aside the question of how much credit first-year presidents deserve for a strong economy — they have less influence than you might think — President Trump’s ratings should be much better. A 4.1 percent unemployment rate, the lowest in 17 years, is more typically associated with a 60-plus-percent approval rating for a first-term president.

Lyndon Johnson is the only other first-term president in the era of modern polling with an approval rating under 50 percent while the jobless rate was below 5 percent. But this came after he’d already been president for about four years (having first finished out John F. Kennedy’s term) and as the Vietnam War began to drag down his presidency.

Mr. Trump started in a far worse position than other incoming presidents. His initial approval rating was in the low-to-mid 40s, while most presidents enter with an approval rating over 60 percent. It was fair to speculate that his approval ratings would gradually rise with the benefit of a strong economy. Perhaps he would even benefit from low expectations, as many suspected he did during the presidential campaign.

But by now the economy would have been expected to lift his approval rating into the 50s, based on an analysis of presidential approval and economic data going back to 1950. This is despite the tendency for presidents’ approval ratings to decline during their time in office. If the economy were to overcome Mr. Trump’s unpopularity and send his approval ratings up, you would think we would have started to see signs of it.

It is certainly possible that the economy — or other good news — will still lift his ratings. But it seems just as likely that Mr. Trump will continue to feel the burden of his time in office. On average, a first-term president’s approval rating drops by about a point per quarter after controlling for inflation and unemployment (and controlling for the large bump George W. Bush received after the Sept. 11 attacks).

Mr. Trump still has some of the advantages that helped him win despite low favorability ratings in 2016. He appears to maintain the support of his base and fairly high levels of Republican unity. Indeed, his favorability ratings are still higher than they were in the weeks heading into the 2016 election, when they were in the mid 30s. Many pollsters aren’t asking the favorability question anymore, but those that do find it roughly equal to his approval ratings (high 30s).

His approval ratings among voters might be higher than among all adults; noncitizens may take a survey but are ineligible to vote, and nonwhite and young voters tend to disapprove of the president but have low turnout rates. National data might not be entirely representative of relatively white battleground states and districts, either.

All of this helps explain why many analysts have been cautious about assessing Mr. Trump’s low approval ratings. If his ratings are as good or better today than they were when he won and when Republicans kept control of the Senate and the House, the argument goes, why shouldn’t they win again?

These points are worth keeping in mind, especially if Mr. Trump’s ratings were to tick back up into the 40s. But the big difference between today and 2016 is simple: Mr. Trump is now the president, and elections tend to be referendums on the party in power. A president’s approval rating is typically a very strong predictor of the results of presidential elections and even a helpful one in congressional elections.

Since 1950, no party has held the House through a midterm election when the president’s approval rating is less than 40 percent. The Republican Party’s considerable structural advantages in the House would at least give them a shot to survive this time, but the growing Democratic advantage on the generic congressional ballot and the G.O.P.’s weak showings in this year’s special congressional elections suggest that the president’s approval rating is weighing on the party in exactly the way one would expect.

And while Mr. Trump’s upset victory in 2016 — defying the pre-election polls that showed Hillary Clinton leading in key battleground states — has given him the sheen of invincibility, his victory was not impressive by most standards.

Fundamental-based models — without taking candidates into account — tended to show that the party out of power was a clear if narrow favorite to win in 2016: The pace of economic growth and President Obama’s approval rating were positives for the Democrats, but that wasn’t enough for the party to be favored because of the burden of seeking the presidency for a third consecutive term.

Mr. Trump had the added advantage of facing Mrs. Clinton, who was under F.B.I. investigation for most of the campaign and ended with the worst unfavorability ratings of any candidate who won a major party nomination other than Mr. Trump, according to Gallup.

Yet in the end, Mr. Trump lost the popular vote by two percentage points, with 46 percent of the vote. It was the second-worst showing since 1948 for the candidate of the party out of power against a party seeking at least a third straight presidential term (after Michael Dukakis in 1988). It was not necessarily a show of strength.

None of this is to say that Mr. Trump’s approval ratings can’t or won’t rise. But at some point, he’ll probably need them to.

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