Republican presidential nominee Donald Trump gives a thumbs up the the crowd during a campaign rally on August 31, 2016 in Phoenix, Arizona. Trump detailed a multi-point immigration policy during his speech. (Photo by Ralph Freso/Getty Images)

The past few weeks have brought a string of polls showing the presidential race tightening — first nationally, now in some key swing states. The most recent poll in every swing state, in fact, has Donald Trump within at least five points of Hillary Clinton.

But one number buried inside a CNN/ORC poll has to be particularly encouraging for Republicans: the generic ballot result.

That question asks voters whether they, as of today, would vote for a generic Republican candidate or a generic Democratic candidate for Congress. Among registered voters, 47 percent picked the Republican, and 46 percent picked a Democrat. Among likely voters, Republicans also led by a slim margin, 49-47.

The poll comes the same week that another pollster — George Washington University — also showed the generic ballot very close, with Democrats slightly ahead, 45-43, among likely voters.

There is limited data on the generic ballot this year, since it’s generally tested closer to an actual election. But both polls represent an improvement for the GOP over recent weeks.

Okay, basically a tie ballgame. So why do we bring this up?

Well, there’s been a large amount of fear in Republican circles that Donald Trump’s candidacy could be an utter disaster for down-ballot Republicans in November. The GOP's Senate majority was already in jeopardy, and there has even been increasing talk about the House being in play, despite the long odds. (Some analysts doubt Democrats could win back the House any time this decade due to how voters are dispersed, and GOP-led gerrymandering.)

As Chris wrote Friday, Republicans have to be encouraged by new polls showing Sens. Marco Rubio (R-Fla.) and Rob Portman (R-Ohio) running strong with clear leads in key states. Those are big races when it comes to avoiding a four- or five-seat loss on a tough map full of GOP-held blue and swing states, and keeping the majority.

And while those polls are good news, the generic ballot numbers are so far indicating Rubio and Portman aren't necessarily the exceptions. They suggest Republicans across the board aren't being dragged down by Trump right now nearly as much as the party feared -- if they're even being dragged down at all.

Now, it should be noted here that the generic ballot isn’t necessarily predictive of actual results. As our own Philip Bump wrote back in 2014, the numbers can vary several points between the final generic ballot of likely voters and the actual voters on Election Day.

But generally, the generic ballot has tipped us off when we have a wave coming. In 2006 and 2008, Democrats had a clear advantage on the generic ballot, and they won big. Same for Republicans in 2010. Those advantages were clear by this point in all three years.

Which brings us to 2014 — another GOP wave year. The generic ballot then was actually pretty close in some polls, but the majority gave Republicans an edge. The Washington Post-ABC News poll on the eve of the election gave Republicans a six-point advantage, and they won the congressional popular vote by seven points.

In other words: It was clear a GOP wave was possible, and it happened.

Democrats can win the Senate without a wave, yes. But that result becomes far less probable if the generic ballot remains anywhere close to a tie. That’s when incumbents in swing states tend to win reelection and the majority party tends to stay in power.

Keep an eye on this poll number over the next couple months. If it’s close to even, Republicans in the Year of Trump will be pinching themselves.