In the RealClear Politics piece, Mr. Cortes wrote that he had believed Republican voters were ready to move on from former President Donald Trump this election cycle, and “I now believe I was wrong.”

Mr. Cortes was an advisor in President Trump’s 2016 and 2020 campaigns.

In May 2023, he announced his endorsement of Mr. DeSantis in a Newsweek editorial, writing that the “America First movement” was bigger than President Trump.

He made a case for Mr. DeSantis as “the best possible option to win the presidency in 2024” with few references to President Trump, but he later criticized the former president on social media.

As the spokesman of Never Back Down, Mr. Cortes was asked about Mr. DeSantis’s stalling poll numbers contrasting with President Trump’s consistent lead. His comment about the governor being “way behind” in the polls during a Twitter spaces event kicked off a spate of coverage about Mr. DeSantis’s embattled campaign.

In October, Mr. Cortes left his position as a spokesperson for Never Back Down but did not withdraw his support for the governor.

“Those of us who backed Ron DeSantis—or the other Republican candidates—should read the room,” he wrote in his new op-ed.

He pointed to President Trump’s victory streak in the polls and most recently in Iowa and said it was time to “coalesce and unite” behind the GOP voters’ favorite.

“We do not have the luxury of further internal strife and instead must gird for an epic battle this autumn against our opponents who are inflicting daily damage upon America,” Mr. Cortes wrote, echoing President Trump’s victory remarks after Iowa, where he called for unity and praised his GOP rivals for a change.

He inferred that voters want Trump because they “admire the resilience of this outsider who is so reviled by the ruling class” and see him as their champion, referencing the spate of legal cases against President Trump as examples of corruption.

Mr. Cortes wrote that time spent attacking President Trump “only dilutes the power of our cause” as the general election draws near.

Mr. Cortes urged unity against a second term for President Joe Biden or Vice President Kamala Harris, pointing to the border crisis and inflation.

“At such a flashpoint in history like this one, political unity among conservatives is an imperative,” he wrote.

“How do we save America? It is time to unify behind former President Trump as he leads the battle against the ruling class and the oligarchs intent on destroying the American way of life.”

Mr. Cortes “pledged” to campaign for President Trump as he “proudly did in 2016 and 2020.”