Colombian voters turned to right-wing parties critical of the country's peace deal with the main leftist rebels and knocked the current president's party down in congressional elections, raising questions about the future of the accord.

Sunday's vote was seen as a barometer for a fiercely contested presidential election in May. It was also the first time former members of the Revolutionary Armed Forces of Colombia, or FARC, competed politically since disarming under the 2016 peace deal to end a half century of conflict. As expected, support for their radical agenda was soundly rejected, with FARC candidates getting less than 0.5 percent of the overall vote. That means their political party will get only the 10 seats guaranteed them by the peace accord.

"The FARC are in a tough spot," said Leon Valencia, a former combatant who now runs the Peace and Reconciliation Foundation, a think tank. "A long war has generated lots of fear and rancor towards them."

By contrast, many of the accord's critics picked up seats, with the Democratic Center party led by former President Alvaro Uribe headed to being the biggest bloc in the Senate. Uribe's hand-picked presidential candidate, Sen. Ivan Duque, easily swept an open primary among three conservative candidates in which more than 5.8 million people voted — a bigger haul than either of the top two finishers got in the first round of the 2014 presidential election.

President Juan Manuel Santos' coalition, which supported the peace deal, struggled. His own Party of National Unity, which was the biggest political movement in the outgoing congress, finished fifth overall.

The results are likely to lead to a last-minute scramble among presidential candidates to form coalitions to better position themselves ahead of what is seen as a wide-open presidential race.

Two candidates under pressure to join forces are Humberto de la Calle, who was the government's chief peace negotiator, and former Gov. Sergio Fajardo. Both candidates have vowed to implement the peace deal. The Green Alliance, one of the parties supporting Fajardo, doubled its vote tally from the last congressional elections, though it only came in sixth overall this year.

Another candidate who has backed the peace deal is Gustavo Petro, a leftist former mayor of Bogota who has promised to raise taxes on the rich and unseat the country's political establishment. Petro won a leftist primary Sunday in which he got 2.8 million votes. It was 1.2 million votes less than Duque's total but still made him a top presidential contender.

"Our results were very positive," Petro told his followers. "The presidential campaign starts today."

Duque has said he would not "thrash" the peace accord with the FARC, but he would attempt to modify certain aspects, like a provision that allows the former rebels with drug-trafficking convictions to participate in politics. He has also called for tougher controls on the FARC's finances.

"A true peace is built through the triumph of the rule of law not through the relativization of justice," he told his followers after election results came in.