ARI SHAPIRO, HOST:
Shortly after the Democratic National Convention this summer, it looked like Republicans on Capitol Hill were in trouble. According to the polls, Democrats were leading in races that could determine control of the Senate. Now with less than six weeks until Election Day, we have an update from NPR congressional reporter Susan Davis. Hi, Sue.
SUSAN DAVIS, BYLINE: Hey, Ari.
SHAPIRO: What do things look like today?
DAVIS: The battlefield has shrunk significantly. When we spoke earlier this summer, there was about 10 or 11 races that made up the Senate battleground. And about four of those have been taken off the table. And that's good news for Republicans because those are Republican-held seats. We're talking about Ohio's Rob Portman, Arizona's John McCain, Florida's Marco Rubio and Iowa's Chuck Grassley. All four of these Republican senators are now pretty much favored to win re-election, and that is good news for them.
SHAPIRO: We've heard from so many Republicans who are not supporting Donald Trump, but are putting their money behind Senate races. Is part of this map shrinking a result of that effort?
DAVIS: Hey, money always helps, right? And you have wealthy Republican donors, like Sheldon Adelson, hedge fund manager Paul Singer and the Koch brothers, who have put tens of millions of dollars into Senate races instead of the presidential. One notable way this money has had an impact is that Republicans have been able to run thousands of more ads in competitive Senate races.
SHAPIRO: Tell me about the seats that are in play.
DAVIS: OK. So Republicans have a 54-seat majority, which means Democrats need to win four seats and the White House because a 50/50 Senate is broken by the vice president. Or Democrats would need to win five seats outright if Donald Trump wins the White House. Democrats are already favored to pick up two of the seats they need in Wisconsin and Illinois. So it's now come down in these final weeks to a throwdown over two, maybe three seats in a battlefield of just five seats.
I should add one caveat. Democrats are trying to make Missouri in play. That's Republican incumbent Senator Roy Blunt. The race has tightened, but it's not quite there yet.
SHAPIRO: What are they?
DAVIS: I call them the core five. They are the races in Indiana, New Hampshire, North Carolina, Nevada and Pennsylvania. All but one of these seats - Nevada - is Republican-held, which simply means Democrats have more opportunities than Republicans do to pick up seats.
Nevada has been another bright spot for Republicans. This is the seat of retiring Senate Minority Leader Harry Reid, so a win here would be particularly fulfilling for Republicans. The Republican candidate is Congressman Joe Hackett, and he is leading in every public poll since July against the Democratic candidate, a woman named Catherine Cortez Masto.
Also, in Indiana, Democrats were hoping that former Senator Evan Bayh, who's making - trying to make - a comeback would walk away with this race. But Republicans have been able to whittle down his lead to single digits, so flipping in the end is going to be a lot harder today than it was a month ago.
SHAPIRO: Six weeks to go. What's the bottom line?
DAVIS: The bottom line is that the Senate battlefield has narrowed dramatically, but it still tilts towards Democrats. Three of those five core Senate races - New Hampshire, North Carolina, Pennsylvania - they're all presidential battlegrounds, too. And they're all statistical ties, although Hillary Clinton is leading in Pennsylvania and New Hampshire, and North Carolina is razor tight. You know, these down-ballot races - they tend to break in the final days and weeks of a national election year. So in the next couple of weeks, it's going to become pretty clear whether a takeover is imminent or if Republicans are going to hold control of the Senate.
SHAPIRO: NPR congressional reporter Susan Davis, thank you.
DAVIS: You bet. Transcript provided by NPR, Copyright NPR.