Marco Rubio. AP Republican presidential candidate Marco Rubio slogged through a tough day of contests Saturday, placing no better than third in each of the day's four races and watching a top rival start to look like a more viable alternative to frontrunner Donald Trump.

Rubio, a Florida senator, appeared as if he would miss out on racking up delegates from two of the four contests Saturday. He also suffered a pair of distant third-place finishes.

Rubio's troubles started in Kansas, where he had secured the endorsement of Gov. Sam Brownback and US Sen. Pat Roberts.

He nevertheless finished in third with just 16.7% of the vote. Texas Sen. Ted Cruz won the state in a dominant display, while Rubio secured just six delegates.

Late in the day Saturday, he placed a distant fourth in Maine — behind Cruz, Trump, and Ohio Gov. John Kasich. Because he did not receive 10% of the vote, he also failed to acquire any delegates.

Early returns also didn't paint a good picture for Rubio in Louisiana — where, with 40% of precincts reporting, according to CNN, he had gotten less than 12% of the vote. That would put him well under the 20% threshold there.

Returns from Kentucky also put Rubio far behind Trump and Cruz in the Bluegrass State.

The results gave Cruz fodder to again ask rivals to "prayerfully" consider dropping out of the race to unify opposition to Trump's candidacy. Rubio has only placed first in one state so far: the Minnesota caucuses.

"What we are seeing is Kansas is a manifestation of a real shift in momentum," he told supporters at a rally in Idaho.

For its part, Rubio's campaign spun the apparent bad night by placing an emphasis on future contests, in which Rubio's team argued that Rubio would be best positioned to compete with Trump. Those contests include the primary in Rubio's home state of Florida, which has become virtually must-win for him.

"Marco has done well in primaries so far. We beat Ted Cruz in Virginia. We beat Ted Cruz in South Carolina. We beat Ted Cruz in Georgia, a state that Ted Cruz originally thought he might actually win," Alex Conant, the Rubio campaign's communications director, said in a Fox News interview.

"So we feel really good about the map moving forward," he added. "And after we win the Florida primary, the map, the momentum and the money is going to be on our side."