If Democrat Jon Ossoff holds his narrow polling lead and wins this traditionally red district, his party will find it easier to raise money and recruit high-quality candidates. Jitters within the Republican caucus will get worse; some vulnerable veteran members will conclude a re-election isn't worth the trouble and retire. An Ossoff victory would also darken the cloud over the House-passed health-care bill, which 6 in 10 voters here, including 3 in 10 Republicans, say they dislike.

Georgia's 6th District has become an early proxy battle for the November 2018 mid-term war for control of the House, and it will immediately shape the climate on Capitol Hill as Republican majorities grapple with President Donald Trump 's agenda.

ATLANTA — The record $50 million lavished on Tuesday's special House election has left this city numb. But considering its impact elsewhere, one side will get its money's worth.

Democratic candidate Jon Ossoff speaks during a visit to a campaign office to thank volunteers and supporters as he runs for Georgia's 6th Congressional District on June 19, 2017 in Sandy Springs, Georgia.

The contest will elect a replacement for Tom Price, the veteran Republican who gave up the seat to become Trump's Health and Human Services secretary. This relatively affluent suburban Atlanta district routinely gave Price easy victories.

Both parties went into Election Day saying the outcome remains too close to call. A high volume of early voting points toward heavy turnout, though weather forecasters predict thunderstorms, which could discourage some voters.

But a victory by Republican Karen Handel would have a calming effect just as the Senate prepares to take up its health-care legislation, which GOP strategists consider vital to averting rebellion within the party's conservative base. And it would deal a discouraging psychological blow to Democrats who have poured so many hopes and dollars into this campaign.

Republican candidate for Georgia's 6th Congressional district Karen Handel speaks to supporters at the Cherokee Cattle Ranch restaurant in Marietta, Ga., on the final day of campaigning on Monday, June 19, 2017.

But Trump barely beat Hillary Clinton in the district, which is heavy with the college-educated voters, Trump's weakest Republican constituency. And that makes it emblematic of the kind of districts Democrats will need to carry to pick up the 24 seats they need next year to make Nancy Pelosi the House speaker again.

The 23 Republican-held House districts where Clinton won last November represent prime Democratic targets in 2018. But they must also generate enough political momentum to win some of the districts she lost. Georgia's 6th is among 12 additional Republican-held districts where Clinton came within 5 percentage points of winning. In 62 other Republican-held districts, Trump received less than 55 percent of the vote.

In a race dominated by national rather than local currents, Trump's recent erosion in the polls helps the opposition party. Some 26 percent of Republicans viewed the president unfavorably in a recent Atlanta Journal-Constitution poll here, significantly higher than in national polls.

Yet since Republicans make up a higher proportion of the district than they do nationally, it's unclear whether that's enough disaffection to nudge Ossoff over the finish line. David Wasserman, a specialist on House elections at the Cook Political Report, says Ossoff needs at least 10 percent of the Republican vote to win.

That's precisely the level of Republican support Ossoff was getting in the Journal-Constitution poll. One late poll released Monday showed Handel with a 2 percentage point lead, backing up the assessment from Handel pollster Whit Ayres that she has gained in the race's closing days.

"I hope that's enough," Ayres said.

The impact of either outcome is impossible to forecast. But this test of partisan strength five months into Trump's term comes as the Senate prepares to take up a still-secret health-care bill.

Senate Majority Leader Mitch McConnell needs at least 50 of his 52 caucus members to close ranks behind Trump's call to repeal and replace Obamacare. Two of them, Dean Heller of Nevada and Jeff Flake of Arizona, face competitive 2018 re-election bids.

Panic after a Republican loss could strain party unity as lawmakers from less conservative districts focus increasingly on self-protection. Yet others from more conservative districts may feel an increased urgency to show core supporters that Republicans can act — not only on health care but also on issues such as tax cuts and infrastructure.

Party leaders, with little margin for error, hope the latter effect would outweigh the former.

"Paradoxically, I think it will help the agenda as it will focus the members on their survival," said former Republican Rep. Vin Weber, now a Washington lobbyist. "Some will try to distance themselves from Trump, but the overriding reaction will be a desire to get some things done they can talk about."