Around this time in 2012, I believed Mitt Romney had a good chance of beating President Obama. I was not alone. The thinking went like this: Obama was unpopular. The economy was sluggish. The Democrats had been drubbed in the previous midterm. Independents did not support the president.

I scoured every new poll and piece of economic data for nuggets that confirmed my biases. Job growth was unsatisfactory, men were dropping out of the workforce, polls sampled more Democrats than Republicans—these notions reinforced my thesis. In late October, when Hurricane Sandy hit New Jersey and the president performed well in a crisis, I began to think Romney would lose. On the morning of Election Day, as I walked to my polling place in Alexandria and saw nothing but Obama-Biden signs, I knew he would lose. And by the time the election was called that night, I understood that I should have been more skeptical of his chances all along.

Why? Because I had dismissed what I had been told in the spring during a lunch at the Brookings Institution. After I explained why Romney could pull it off, one of the political scientists at my table stroked his beard and said, "Look, it’s an interesting story you tell, but what matters is approval and the state of the economy. That’s what will reelect President Obama." My own disapproval of the president and disappointment in his economic policy led me to short his advantages.

It’s a mistake I do not want to make again. And so, as you see the polls showing Donald Trump competitive or in some cases slightly ahead of Hillary Clinton, it’s important to look at the more fundamental numbers of President Obama’s job approval, the unemployment rate, and the generic congressional ballot. The comparison does not bode well for Trump. Republicans should worry.

Presidential Approval. Four years ago, President Obama had an approval rating of 46 percent in the Gallup tracking poll. His disapproval rating was also 46 percent. The Real Clear Politics polling average had him at 48 percent approve, 48 percent disapprove. Troubling numbers. He won anyway.

Where is he now? The most recent Gallup tracking has President Obama at 52 percent approval, 44 percent disapproval. The Real Clear Politics average is tighter: about 49 percent approve to 48 percent disapprove. For the sake of comparison, President Bush was at 28 percent approval this week in 2008.

So, the public views the president at least as well as, and in some cases more favorably than, it did when it reelected him four years ago. That would favor the nominee of his party.

The Economy. Part of the reason President Obama’s numbers have improved, in my opinion, is that he has been out of the news. But most of the reason has got to be the economy. It’s getting better. The average fuel price in the early summer of 2008 was $4.00 a gallon. When Obama was reelected four years later, the average was $3.61. Today the average price is $2.32.

The unemployment rate in April of 2012 was 8.1 percent. By April of 2016, the rate had fallen to 5.0 percent. Most extraordinarily, April was the seventy-fourth consecutive month of job growth under this administration. As the country has approached full employment, the tightening labor market has led to expected increases in personal income and consumer spending.

No one is saying the economy is perfect. No one is saying President Obama is wholly responsible for the improvement. What’s undeniable is that the picture has brightened since the Democrats won the elections of 2008 and 2012. Voters tend to reward that track record by sticking with the incumbent party.

Generic Ballot. Four years ago, the Democrats and Republicans were basically tied in the Real Clear Politics average of the generic congressional ballot. Today, the Democrats are pulling ahead of the Republicans. It’s a bad sign for the GOP.

Clinton vs. Trump. Let’s not forget the candidates. They matter too. A bad candidate can make the difference in a closely fought election. Look at how Bruce Braley lost to Joni Ernst in 2014.

What’s interesting about 2016 is that neither party has a good candidate. Both Donald Trump and Hillary Clinton are disliked and distrusted—more so than any other nominees in history.

Trump supporters point to Clinton’s unpopularity as reason to think he can win. But they forget that, as unpopular as Clinton is, she is still more popular than Trump. They forget that, when neither candidate is stellar, an election reverts to the fundamentals. Which help the Democrats.

There’s a question mark, though. Right now the Democrats are divided between Clinton and Bernie Sanders. The assumption has been that eventually Sanders and his voters will support Clinton and expand her lead over Trump. But what if that doesn’t happen? What if, as seems to be the case, Bernie Sanders is a fundamentally unserious and self-destructive politician who will not cede the nomination without a struggle? He could split the Democrats to Trump’s advantage.

It’s an unlikely scenario. But keep it in mind. Otherwise the Democrats will come home, the candidates’ negatives will cancel out, and the popular incumbent and improving economy will make Hillary Clinton the next president. Barring a stunning outside event, the question won’t be whether she’ll win. It will be by how much.