• A close win for either Democratic former Gov. Terry McAuliffe or Republican Glenn Youngkin could signal a rough road ahead for Democrats heading into next year's midterms. 
• Pollsters and politicians are looking to the off-year election in Virginia as a predictor of next year's midterms.
• Polls have shown a tight race, with momentum shifting toward Youngkin in recent weeks.

Virginia's high-stakes governor's race between Democrat Terry McAuliffe and Republican Glenn Youngkin is coming down to the wire as voters go to the polls on Election Day.

But the tight election is expected to yield important clues beyond Virginia about the nation's political landscape going into the 2022 midterms and beyond. Polls close at 7 p.m. ET.

Pollsters and politicians are looking to the off-year election in Virginia as a predictor of next year's midterms, when Democrats will try to maintain their thin majorities in the U.S. House of Representatives and U.S. Senate.

"There have been four times when the party that's been on the outs has won the House from the incumbents, four times in the last 50 years," veteran GOP pollster and strategist Frank Luntz told CNBC on Tuesday. "Every one of those four times, 100% Virginia has predicted the outcome, which is why everybody's watching it so closely."

In one scenario, McAuliffe will come out on top and be elected to his second, non-consecutive term as governor of the commonwealth. McAuliffe's strategy of aggressively linking his well-financed GOP opponent to former President Donald Trump will be used by Democrats as template for future campaigns to employ. 

In another scenario, Youngkin, a former Carlyle Group CEO, will secure a first-in-a-decade victory for Republicans. His Democratic opponent will be criticized for focusing too much of his campaign on Trump, and Youngkin will be hailed for showing that it is possible for a GOP candidate to win the governor's seat in a blue-leaning state while keeping the former president at arm's length.

While no one can be sure of the outcome until after polls close Tuesday night, some experts say one thing will be clear after this race, regardless of election results: Democrats are facing an uphill battle. 

"Democrats are going to struggle to maintain their very thin majorities in the House, especially in the midterms, regardless of what happens in this Virginia gubernatorial race," said Karen Hult, a political science professor at Virginia Tech. 

Momentum has shifted toward Youngkin. Polling has tightened in recent weeks, showing the candidates neck-and-neck in the race that was expected to be a relatively easy win for Democrats. President Joe Biden won the state by 10 points in 2020.

A Washington Post-Schar School poll released Friday found McAuliffe leading his Republican opponent by a mere one percentage point, well within the poll's margin of error of four percentage points. And a week earlier, a Monmouth University poll found the candidates with identical levels of support at 46%. 

If these polls turn out to be accurate, McAuliffe or Youngkin could win by a few percentage points, which would signal a rough road ahead for Democrats heading into next year's midterms. 

"Polls consistently show that this race is within the margin of error," said Stephen Farnsworth, a professor of political science at the University of Mary Washington in Virginia. "The closeness of the contest is bad news for Democrats, given that Joe Biden won Virginia by ten points a year ago."

If Youngkin wins the race by a meager two points, as the Harvard Political Review predicts, the Democratic party would be 12 points behind their 10-point win in 2020. 

If McAuliffe wins by two points, as Race to the WH predicts, the Democratic party would still be eight points behind their 2020 victory. 

Either close outcome would leave Democrats well behind Biden's 10-point edge.

Experts say the tight race could be a sign that Biden's declining popularity is having a trickle-down effect on the Democratic Party. The Washington Post-Schar School poll showed the president's job approval ratings underwater in Virginia at 46%. And the Monmouth University poll found Biden's job approval rating at 43% among Virginians. 

The numbers echo the overall national decline in Biden's job approval ratings and follow a rough summer and fall when Biden grappled with a spike in Covid cases, fallout from the chaotic withdrawal from Afghanistan and a messy fight to reach a deal with his own party on his legislative agenda. 

A narrow win for either candidate could indicate that Biden's declining popularity and Democratic infighting has stymied voter enthusiasm about the party overall. 

For example, the Monmouth University poll found that Youngkin's supporters are more excited than McAuliffe's to vote in the upcoming election by nearly 23 percentage points.

"The promise of the Biden presidency—knowledge, competence, and stability in tough times—have all been called into question," Democratic pollster Jeff Horwitt of Hart Research Associates told NBC News.

On Tuesday, the president dismissed any connection between between his job approval ratings and the results of Virginia's governor's race.

"I don't believe and I've not seen any evidence that whether or not I am doing well or poorly, whether or not I've got my agenda passed or not, is going to have any real impact on winning or losing," Biden said at the COP26 press conference in Glasgow, U.K.

Biden added that he believes Democrats will prevail in Virginia and New Jersey, where Gov. Phil Murphy is also on the ballot.

"We're going win," the president said at the press conference. "I think we're gonna win in Virginia. We all knew from the beginning, this will be a tight race and it is."

"I think we are going to win New Jersey as well," he continued. "I hope that every eligible voter in Virginia in New Jersey shows up and votes."

Regardless of which candidate wins, a close outcome in Virginia could also signal that Democrats can't count on playing the Trump card. 

The former president, who has endorsed Youngkin, continues to be more unpopular than Biden in Virginia and nationally.

McAuliffe has tried to leverage this and take any opportunity to link his Republican opponent to Trump, citing their overlapping stances on Covid-19 and critical race theory, among other contentious issues. Even so, McAuliffe told reporters on Saturday that the election is "not about Trump," CNN reported.

Meanwhile, Youngkin has maintained his distance from Trump while also leaning into some of the former president's rhetoric to motivate Virginia's GOP base. 

A narrow win could indicate that keeping the former president at the forefront of the governor's race did not "energize" Democrats like it did during the Trump presidency, according to Farnsworth.

Opposition to Trump sparked high turnout from Democrats during his presidency, which fueled a blue wave that helped Democrats win back the House in 2018 and propel Biden to victory last year.

"The Democratic Party's main problem in this election cycle was that former President Trump does not energize the party base the way he did when he as President Trump," Farnsworth said.

Still, Democrats claimed a substantial lead in early voting, making up roughly 53% of the 1.1 million Virginians who sent in their ballots before Election Day, according to the latest data from Democratic data firm TargetSmart. 

The rest of Virginia voters will have a chance to head to the polls Tuesday from 6 a.m. to 7 p.m. ET. Mail-in ballots must be postmarked by 7 p.m. that day and received by noon on Nov. 5.

Virginia, which has historically reported election results quickly, will likely determine election results just a few hours after polls close, Farnsworth said. However, if the margins are razor thin or there are issues with provisional ballots, results may not come out on Tuesday night.