"If this race turns out to be closer than what the polls are indicating right now, the chances of a contested election are high," said Peter Cardillo, chief market economist at First Standard Financial. "That means the saga of this election does not end tomorrow."

According to an analysis of quarterly conference call transcripts conducted by Reuters, executives from more than 80 companies have referenced the election as a challenge to their performance. To the extent that the grueling presidential campaign has had an impact on business, economists warn that a contested result could continue to act as a brake on the market's momentum.

"Any time there's uncertainty, markets will react," said Lawrence J. White, an economics professor at New York University's Stern School of Business. Unlike previous business-friendly GOP candidates, Trump's hostility to globalism and his threats to reverse trade agreements have pushed companies into a holding pattern that has kept financial markets on edge.

After a slugfest of a campaign, voters are likely happy that Election Day will bring the whole ugly spectacle to rest. Unless, of course, a Clinton win is contested by Donald Trump or his camp. Such a situation would have economists and investment pros, as well as voters, reaching for the antacid.

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Marcus Noland, executive vice president and director of studies at the Peterson Institute for International Economics, said if the electoral votes were close and a key state like Florida came in with a razor-thin margin for Clinton, Trump could push for a recount. "You could end up back in 2000, but it could be much nastier," he said.

Even a contested election that ultimately ends in Clinton's favor could do longer-term damage, White said. "He very likely won't succeed, but just the possibility that he might, or that this might adversely affect Clinton's ability to get along with Congress her first session — those would be not favorable outcomes as far as the market is concerned," he said.

Uncertainty breeds volatility

That's bad news for everything from equities to precious metals to currency, which have already been gyrating at the election's last-minute plot twists.

"What's really striking to me is how the market seems to be an inverse indicator of Trump's fortunes," Noland said. "With each twist and turn, the market is moving." After falling last week in the wake of the FBI's announcement that it was investigating additional Clinton emails, the agency's weekend announcement that it hadn't uncovered anything game-changing sent the markets back up on Monday.

"If you're not able to remove uncertainty, that poses problems," said Andy Smith, senior vice president of financial planning at investment-planning firm Financial Engines. "It's more of the same kind of holding pattern until you get resolution."

The long-range forecast

"That would be certainly damaging for hiring, for employers who are trying to forecast where their businesses will be not only in the short term over the next six months or so, but in the longer term," said John Challenger, CEO of executive outplacement firm Challenger, Gray & Christmas.

The longer it takes that resolution to come, the more lasting the effect on an economy whose current expansion might already be on borrowed time.

"When you've been in a long running cycle of economic upswing, there are fears that there's a recession on the horizon," Challenger said. "No one knows what that catalyst could be."