Sen. Ted Cruz on Saturday bolstered his case that he is the strongest Republican alternative to Donald Trump, topping the party's presidential front-runner in caucuses in Kansas and Maine.
Mr. Cruz's victories came in Republican-only contests that forbid the participation of independent voters, who had helped spur the New York businessman's success in other states.
Caucus results haven't yet been reported in Kentucky's GOP caucuses or the primary in Louisiana, where polls close at 9 p.m. ET.
Mr. Cruz said his victories should be an impetus for other rivals trying to become the GOP's Trump alternative to end their campaigns.
"We'll continue to amass delegates, but what needs to happen is that the field needs to continue to narrow," Mr. Cruz told reporters traveling with him in Idaho, where he was campaigning before the state's Tuesday primary. "As long as the field remains divided, it gives Donald an advantage."
Mr. Cruz won a commanding victory in Kansas, taking 48% of the vote to 23% for Mr. Trump. Sen. Marco Rubio had nearly 17%, and Ohio Gov. John Kasich had 11%.
In Maine, Mr. Cruz had 46%, while Mr. Trump had 33%. Mr. Kasich was in third place with 12%.
With the Kansas and Maine victories, Mr. Cruz has won six states, the second-most after Mr. Trump's 10. Mr. Rubio has one just one state, Minnesota.
"We have beaten Donald not once, not twice," Mr. Cruz said on Saturday.
Heading into Saturday, Mr. Trump led the Republican field with 329 delegates. Mr. Cruz was second, with 231 delegates, while Mr. Rubio was third, with 110 delegates.
Mr. Kasich had 25 delegates. Ben Carson suspended his campaign on Friday.
There are 155 delegates at stake on Saturday. Kansas will award 40, Kentucky and Louisiana will award 46 each and Maine has 23. Mr. Cruz won 12 of the Maine delegates, while Mr. Trump will get 9 and Mr. Kasich two.
It takes 1,237 delegates to clinch the Republican nomination.
Mr. Cruz's Kansas blowout also serves to further diminish Mr. Rubio. He finished a distant third in the state and failed to carry even the wealthy Kansas City suburbs, the type of area that Mr. Rubio has targeted and where he has done well in other states. Mr. Rubio carried just 13.7% of the third congressional district's vote.
Mr. Rubio's poor performance wasn't for lack of effort. He had cancelled Friday events in Kentucky and Louisiana to instead make three stops in Kansas, where he had support from the state's leading political figures, including Gov. Sam Brownback, Sen. Pat Roberts and former Senate Majority Leader Bob Dole.
At a campaign stop In Puerto Rico, which holds a Sunday primary, Mr. Rubio played down Saturday's results and said he is focused on the March 15 Florida contest.
"There will be more delegates awarded in Florida than basically every state that voted today combined," Mr. Rubio said at a San Juan news conference.
Florida awards 99 delegates. There were 155 delegates at stake Saturday.
Mr. Trump also mounted an effort in Kansas. He had cancelled a planned appearance Saturday at the Conservative Political Action Conference in suburban Washington to instead hold a campaign rally in Wichita and appear at a caucus site.
In addition to his Kansas and Maine victories, Mr. Cruz also won a straw poll at CPAC, with 40% support. Mr. Rubio placed second, with 30%. Mr. Trump was third, at 15%.
Tim Miller, a spokesman for Our Principles PAC, the super PAC devoted to stopping Mr. Trump's political rise, said the results in Kansas and Maine are evidence the group's efforts are working.
"The anti-Trump momentum is building, as he is now even further away from garnering the majority of delegates necessary to win the nomination, " Mr. Miller said. "Historically, the party's nominee has built support and coalesced with other factions as the process goes on. Donald is going the other direction."
The Cruz victory comes two days after 2012 GOP nominee Mitt Romney urged Republicans to band together to stop Mr. Trump from winning the party's nomination. Mr. Romney's prescription called for strategic voting, backing Mr. Rubio in his home state of Florida, Mr. Kasich in his native Ohio and Mr. Cruz in states where he is strong.
Ohio and Florida hold primaries March 15 in which the winners receive all of the state's delegates, meaning that Mr. Rubio or Mr. Kasich, if they were to win, would take a big bite out of Mr. Trump's delegate lead. Illinois and Missouri also hold primaries that day, though delegates in those states will be awarded proportionally based on the results.
Messrs. Kasich and Rubio appear to be following Mr. Romney's advice. Mr. Kasich said Thursday in Detroit that he would focus his campaign on Ohio, and Mr. Rubio is set to do the same in Florida.
Mr. Cruz has shown no sign of ceding states to his rivals. His campaign announced late Friday that he would open 10 field offices in Florida. The Texan said Saturday he is playing to win there.
"We are competing vigorously in Florida," Mr. Cruz said Saturday. "We will be campaigning on the ground in Florida. We've got a great base of support in Florida."
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