Republican Rep. Dave Brat is trailing Democrat Abigail Spanberger by 5 points in a Virginia district that hasn't sent a Democrat to the House in more than 45 years, according to a new poll.

Spanberger has the support of 47 percent of potential voters, compared to Brat's 42 percent, according to a Monmouth University survey released Tuesday. Spanberger's lead is just outside the poll's margin of error, which is 4.9 percentage points.

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Virginia's 7th Congressional District used to be solidly red, but courts forced the state to redraw it shortly after Brat was elected in 2014 following a shocking GOP primary defeat of then-House Majority Leader Eric Cantor Eric Ivan CantorThe Hill's Campaign Report: Florida hangs in the balance Eric Cantor teams up with former rival Dave Brat in supporting GOP candidate in former district Bottom line MORE. President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE won the district by 6 points in 2016.

Spanberger's lead in the new poll comes from support in Chesterfield County and Henrico County, two Richmond suburbs. Brat leads by 22 points, 57 percent to 35 percent, in the other parts of the district, according to the poll.

Patrick Murray, director of the Monmouth University Polling Institute, called the race a "tale of two districts."

"The Richmond suburbs that backed Clinton in 2016 support Spanberger while the Trump strongholds are firmly behind Brat," he said. "The reason this race is so close right now is because there are more voters in the suburban areas."

The poll's results are based on interviews with 400 potential voters in the district from Sept. 15 to 24.

The nonpartisan Cook Political Report rates the race as a "toss-up." FiveThirtyEight gives Brat about a 70 percent chance to win his reelection bid.