U.S. Sen. Cory Gardner’s early endorsement of President Donald Trump’s 2020 re-election bid earned the Colorado Republican a thank-you from the president.

“Thank you to Senator Rob Portman and Senator Cory Gardner for the early and warm endorsement. We will ALL WIN in 2020 together!” Trump tweeted Friday.

Portman, R-Ohio, also has endorsed Trump in his quest for a second term.

Gardner told the Washington, D.C.-based Independent Journal Review this week that he was endorsing Trump, a reversal after he opposed Trump’s election in the final days of the 2016 race.

Widely seen as the most vulnerable GOP incumbent in 2020, Gardner told the conservative publication in an article published Wednesday that he would back Trump this time.

“I know what Kamala Harris and I know what Bernie Sanders will do to Colorado, and that’s why I’ll be supporting the president,”  Gardner said, citing the California and Vermont senators who are possible contenders for the Democratic Party’s presidential nomination.

He did not mention two other potential Democratic candidates: His fellow Colorado senator, Michael Bennet; or former Colorado Gov. John Hickenlooper.

Hillary Clinton won Colorado by 5 percentage points in 2016, and Democrats swept every statewide race there in 2018 in what was widely seen as a rebuke to Trump.

Gardner opposed Trump during the 2016 GOP primary. He eventually endorsed Trump, but he quickly rescinded that after a tape surfaced in which Trump bragged of sexually assaulting women. Gardner said he would write in the name of Mike Pence, Trump’s vice president, instead.

After 2016, however, Gardner became the head of the arm of the Republican Party that oversees Senate races. He helped engineer the party’s strategy of clinging to Trump in conservative states, which helped the GOP gain two Senate seats while losing control of the House of Representatives in November.

Portman also declined to back Trump in 2016.

The Associated Press contributed.