Minnesota Senate candidate Jason Lewis underwent emergency surgery Monday morning after being diagnosed with a severe internal hernia.

Doctors said the hernia could be "life-threatening if not treated quickly," Lewis' campaign manager Tom Szymanski said in a statement. 

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"Prior to being taken to the operating room, Jason was in good spirits, optimistic, and true to form, he was speculating about when he could resume campaigning, eager to continue fighting for his fellow Minnesotans," Szymanski said in a statement. "Please join me in praying for a successful surgery and a quick and speedy recovery for Jason. Our campaign will release more information as it becomes available."

Jason Lewis, Republican candidate for Minnesota's 2nd Congressional District, is interviewed in CQ Roll Call offices, June 17, 2016. (Tom Williams/CQ Roll Call)

Jason Lewis, Republican candidate for Minnesota's 2nd Congressional District, is interviewed in CQ Roll Call offices, June 17, 2016. (Tom Williams/CQ Roll Call)

Lewis' opponent, incumbent Democratic Sen. Tina Smith, wished him well on Monday.

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"Archie and I are wishing Jason Lewis a successful surgery and a speedy recovery," Smith wrote on Twitter, referring to her husband, Archie Smith.

The Minnesota Senate race narrowed substantially before the election, with Smith shedding her double-digit lead over Lewis, according to a polling average from RealClear Politics.

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Despite Democratic worries, however, Smith's fundraising has reportedly dwarfed the Republican Lewis' with $14 million as of Sept. 30, compared to Lewis' $5 million.

Fox News' Sam Dorman contributed to this report.