On Tuesday, Fox News political contributor Karl Rove threw cold water on Sens. Bernie Sanders', I-Vt., and Elizabeth Warren's, D-Mass., 2020 candidacies.

His comments came after the University of New Hampshire released a poll showing Sanders beating former Vice President Joe Biden by double digits — 30 percent to 18 percent of likely Democratic voters in the granite state. Indiana mayor Pete Buttigieg came in third with 15 percent while Warren lagged each of them with just five percent of likely voters' support.

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Although Sanders has frequently led declared Democratic candidates, Biden, who is expected to declare his candidacy in the coming days, has beaten him in previous polling. "Gotta be a little careful with these polls," Rove told "America's Newsroom" host Bill Hemmer.

Rove pointed to St. Anselm College's earlier polling which showed Biden leading Sanders by 7 percent (23 to 16 percent) among registered Democratic voters in New Hampshire, and Warren garnering 9 percent of their support.

"These numbers are all over the board. Do we really think that Joe Biden has lost 20 percent of his support in 10 days? Do we really think that Bernie Sanders has doubled his support in 10 days? ... Elizabeth Warren, do we think she's lost nearly half her support in 10 days?" Rove asked, sounding incredulous.

Rove, who speculated Sanders could beat President Donald Trump in 2020, said he expected Sanders to have an advantage over Biden given that his home state of Vermont is adjacent to New Hampshire. The interesting story, Rove said, was that Warren, who has been painted as a progressive hero, wasn't doing so well.

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"Elizabeth Warren, just off of a re-election campaign in Massachusetts, not doing too well in either poll," Rove observed. The polling results came just after Warren became the first Democratic candidate to call for impeachment hearings surrounding Trump's conduct in office — something more established Democrats have shied away from apparently due to its political implications.

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Sanders has backed away from impeachment but, like Warren, has faced criticism for proposing large government programs that would cost American taxpayers a lot of money. His populist disposition has led some to compare him to the president. As Rove pointed out, a fraction of Sanders' supporters backed Trump in the general election.

Rove argued that Buttigieg, whom he saw as a strong contender in recent polling, made a smart move in tying Sanders and Trump together as populist influences that needed to be tamed by a candidate like him.