(Reuters) - A crowded U.S. Senate race in Republican stronghold Mississippi could set the stage for weeks of uncertainty over which party ends up controlling the upper chamber of Congress after the Nov. 6 elections.

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Two Republicans and two Democrats are contesting a special election to serve out the remainder of retired Republican Senator Thad Cochran’s term. Under state law, if no one gets 50 percent of the vote, the top two candidates regardless of party affiliation will go to a Nov. 27 runoff.

It is a scenario that could focus international attention on the Southern state and bring in millions of dollars from outside political groups.

“Mississippi could be the deciding factor in who controls the Senate,” said Melissa Scallan, a spokeswoman for Republican U.S. Senator Cindy Hyde-Smith, who was appointed by Mississippi’s Republican governor to temporarily replace Cochran after he retired on April 1.

Democrats, who currently control 49 of the 100 seats in the Senate, face a tough political map as they are defending Senate seats in 10 states that Republican President Donald Trump carried in the 2016 election.

Opinion polls show Hyde-Smith, a former Democrat who has been endorsed by Trump, as the front-runner in the race. Democrat Mike Espy, a former congressman and agriculture secretary in the Clinton administration, is in second place and drawing enough support to possibly make it into a runoff.

Mississippi State Senator Chris McDaniel, a conservative Republican firebrand who tried to unseat Cochran in 2014, is third in the polls, with Democrat Tobey Bartee a distant fourth.

Although Mississippi has not sent a Democrat to the U.S. Senate since 1982, some observers say the increased attention and advertising prompted by a runoff could result in unusually high voter turnout that makes it more of a horse race.

Turnout was cited as a key factor in Democrat Doug Jones upset victory in the U.S. Senate special election in neighboring Alabama last year.

“If the Senate is in play, then Mississippi is ground zero for everything,” said a Democratic Party source who was not authorized to speak publicly.

Mississippi State University political scientist Marty Wiseman said a win by Hyde-Smith on Nov. 6 might dampen enthusiasm among McDaniel’s more populist supporters, potentially opening a window for Espy.

“There’s a lot of speculation that McDaniel’s people will stay home and fuss about their fate,” Wiseman said.

A recent NBC/Marist poll showed Hyde-Smith with 38 percent support of likely voters, Espy with 29 percent and McDaniel at 15 percent. Bartee was supported by 2 percent of respondents.

McDaniel’s campaign did not immediately respond to requests for comment.