But the endorsement is not without caveats. The board acknowledges Rubio could use more experience, and that “we wish he followed the lead of colleague Chuck Grassley and rarely missed a vote in the Senate.” It also outlines a number of unanswered questions on the senator’s policies, and notes that in recent weeks he has taken a more pessimistic tone.

“At his best, Rubio offers an uplifting message of a ‘new American century,'” the board writes.

“Yet more recently, he has pandered to rising pessimism in his party. He talks gloomily about ‘a nation in decline,’ saying President Barack Obama ‘has deliberately weakened America.’ He wants to fight the battles of the past, such as the Supreme Court’s same-sex marriage ruling.”

The endorsement concludes: “We hope Marco Rubio and his party take a different path, one that can lead to the opportunity and optimism he so eloquently articulates.”

The Des Moines Register has endorsed a candidate every cycle since 1988, and only three times picked the eventual winner of the caucuses. Last cycle, it endorsed Mitt Romney, who eventually won the GOP nomination but narrowly lost to Rick Santorum.

Rubio’s taken third place in most polls of the Iowa GOP field, and his advisers acknowledge that’s where they’d like him to finish, aware that it will be difficult at this point to overcome the significant support frontrunners Donald Trump and Ted Cruz have amassed in recent weeks. Iowa, they note, was never a perfect fit for Rubio in the first place, with its Evangelical and social-conservative voting base.

But the endorsement could help Rubio coalesce support among more establishment-minded voters and cement his third-place position in the final vote.

Still, that’s where the endorsement could be somewhat of a double-edged sword for the senator, as it will offer opponents fodder to frame him as establishment — a label he’s resisted over the course of the campaign, as he tries to cobble together a block of support from both conservatives and moderates. And in a cycle where voters seem to be revolting against the establishment and searching for anything but politics as usual, the establishment label could be problematic for any candidate where it sticks.

Indeed, Cruz tagged both Rubio and Trump with the label with comments this week that the “Washington establishment is abandoning Marco Rubio” and supporting Trump instead. Rubio fought back hard against his assessment, saying on Thursday he’s been battling the GOP establishment since his Senate run in 2010, and the amount of money his rivals were spending against him showed he’s in the thick of that same fight again.

“I’ve had over $20 million spent attacking me. That’s not grass-roots money, that’s money from the establishment,” he said.