The final unresolved House race of 2018 is set to conclude Sept. 10 when Marine Corps veteran Dan McCready, a Democrat, faces off against Republican state Sen. Dan Bishop. And although Democrats already rocketed into the House majority last November, this do-over election means much more for the Republicans, who are desperate to avoid an embarrassing setback in a critical 2020 state.

North Carolina's 9th District, anchored by Charlotte's suburbs, shouldn't be a toss-up: in 2016, President Donald Trump carried it 54 percent to 42 percent, more than triple his statewide margin of victory. Yet, the "Battle of the Dans" is going down to the wire.

Dan Bishop, the Republican candidate for senate in North Carolina's 9th District, speaks with supporters in Hope Mills on Aug. 10, 2019. Tom Williams / CQ-Roll Call file

Last November, Republicans thought they had held this seat when GOP nominee Mark Harris, a Baptist minister, led McCready by 905 votes. But Harris' apparent win was thrown out after the state Board of Elections uncovered evidence that one of his consultants had committed absentee ballot fraud. In May, Republican voters chose Bishop, an attorney best known for sponsoring North Carolina's so-called "bathroom bill," as their new nominee.

McCready, a solar energy businessman and a moderate Democrat, has been running here since 2017 and has enjoyed an organizational and financial head start. At the end of June, he had $1.7 million in the bank to Bishop's $344,000. Pro-Republican outside groups, including the National Republican Campaign Committee and the Congressional Leadership Fund, have sought to level the score by spending more than $4 million attacking McCready in the home stretch.

Dan McCready, a Democratic candidate for North Carolina's 9th District, talks with voters in Pembroke on Aug. 10, 2019. Tom Williams / CQ-Roll Call file

Underscoring the importance of the race, Trump — who has endorsed Bishop — is scheduled to campaign for him at a rally in Fayetteville the day before voters go to the polls. Despite the signs of GOP concern, there are three reasons why a McCready victory would still be an upset:

Bishop has a political base in a key part of the district. In November 2018, McCready carried Mecklenburg County, home to the district's close-in Charlotte suburbs, by roughly 9,200 votes. But Bishop simultaneously won re-election in a district largely overlapping that territory 52 percent to 48 percent. If Bishop can neutralize the congressional race in his own backyard, it would be difficult for McCready to build a victory margin elsewhere. Polling in the contest has suggested more upside for Bishop. In late July, an internal poll conducted by ALG Research for McCready's campaign found the contest tied at 46 percent. But the poll also found McCready began the race far better known than Bishop, indicating Bishop probably has more room for his support to grow — especially considering the 9th District voted for Trump by double digits. Democrats might not feel as much urgency as they did in 2018. In the only special election of 2019 so far, Republican Fred Keller captured Pennsylvania's 12th district by 36 points, almost exactly matching Trump's 2016 margin of victory there. That was a departure from special elections held in 2017 and 2018, when Democratic voters were energized to flip control of the House as a check on the president.

The bottom line: Fresh off losing their majority and beset by a new wave of retirements, Republicans badly need a morale boost. A loss Sept. 10 would mean that they would need to gain 20 seats (rather than 19) to reclaim the House majority next year.

But it's not just about the House: Trump's re-election depends on North Carolina, and a Democratic upset would be a genuine sign of danger for the president heading into 2020.