Updated

Marco Rubio may have two campaign victories under his belt in Minnesota and Puerto Rico, but his worried supporters are looking past the silver lining and staring at the dark cloud that has been hanging over his campaign.

The U.S. senator from Florida, who generally has won raves for his debate performances and eloquent speeches on the campaign trail, seems unable to duplicate that success at the ballot box, falling short in 18 of 20 state presidential contests so far.

And while Rubio has downplayed the failures by saying that the most Rubio-friendly states are still to come, polls measuring Michigan and Florida GOP voter sentiment aren't especially promising.

A Monmouth University poll of Michigan GOP voters released on Monday showed Rubio in fourth place, behind Donald Trump, Ted Cruz and John Kasich.

To get any delegates in the Michigan primary, which is Tuesday, a candidate must get at least 15 percent. The poll of likely GOP voters showed Rubio getting just 13 percent.

Another Monmouth poll, of likely GOP voters in his home state of Florida, which votes March 15, had him trailing Trump by 8 points, 38 percent to 30 percent.

He has been closing the gap on Trump, but that gives little comfort to Rubio supporters who worry about even a narrow loss in the winner-take-all, 99 delegate primary.

The anxiety in Rubio's camp has led to a two-day retreat this week in Miami for his top donors, according to Politico, which referred to it as a “leadership huddle” at which they will be meeting with the candidate's top aides. Politico added that the campaign would not address the topics up for discussion.

After Rubio’s disappointing third-place finish in Kansas, on the heels of a poor Super Tuesday showing, supporters publicly expressed bewilderment.

“I felt I had a dog in the fight, and it hurt me personally when I thought we were going to win,” Sen. James M. Inhofe of Oklahoma told the Washington Post. “The thing is, when Rubio was there [in the state], the enthusiasm was so great, better than the others. He had a great reception. If everything had been equal in terms of appearances and organization, he would have won Oklahoma.”

Instead he finished third behind the winner Cruz and Trump.

Rubio insists he feels "real good about the map as we move forward," telling the Associated Press on Sunday that he believes voters across the GOP spectrum want "an optimistic message of conservatism," not just the "anger and frustration" Trump has tapped into.

Rubio campaign officials also have said Florida races can swing quickly, especially when backed by a sustained advertising blitz. They point to the 2012 GOP primary when eventual nominee Mitt Romney surged past Newt Gingrich in part on the strength of $8.8 million in anti-Gingrich ads by a pro-Romney group.

Heading into the week, the top Republican advertiser in Florida was Conservative Solutions PAC, a group promoting Rubio, which this month planned to spend more than $4 million attacking Trump. Three other anti-Trump groups plan to spend a combined $4 million attacking the billionaire front runner before the March 15 primary.

Still, doubts linger.

"Super Tuesday came and Rubio didn't do as well as some of us hoped. So people are saying, 'Let's see how this thing shakes out,'" said Craig Duchossois, who contributed $500,000 last year to a group that backed former Florida Gov. Jeb Bush.

"I'm holding back," the Chicago-based investor said of his own plans.

The campaign, say supporters, has been slow to react to attacks, unable to strongly convey its message or to play up Rubio’s strengths, the Post reported.

Even a Florida win for Rubio would likely leave him unable to get 1,237 delegates needed for the GOP nomination, meaning he’d need a Hail Mary moment at the Republican national convention in July in Cleveland.

“His campaign hasn’t been able to keep up with his candidacy,” Scott Reed, chief political strategist for the U.S. Chamber of Commerce, told the Post. "They don’t have the operation in the states to help him get over the top. He should be a finalist going all the way to California, and he’s not.”

The Associated Press contributed to this report.

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