"Morning Joe" co-hosts Joe Scarborough and Mika Brzezinski joined Stephen Colbert on "The Late Show." Scarborough announced that he could no longer support the Republican Party because of its allegiance to President Trump. (Erin Patrick O'Connor/The Washington Post)

Roughly two hours before CBS aired Stephen Colbert's interview with Joe Scarborough and Mika Brzezinski on Tuesday's episode of “The Late Show,” Fox News host Sean Hannity complained to his viewers about “Liberal Joe.”

Hannity has been using the moniker for a while in an apparent attempt to weaken the former Republican congressman's GOP bona fides. The weight of Scarborough's criticism of President Trump is rooted in the idea that it comes from a member of Trump's own party. Hannity has been trying to destroy that premise by arguing that Scarborough is really just another liberal on MSNBC and that Republicans should not think of him as one of their own.

Scarborough made Hannity's job easier when he told Colbert that he is officially leaving the GOP.

“I’m not going to be a Republican anymore,” the “Morning Joe” co-host said. “I’ve got to become an independent.”

Scarborough isn't ready to call himself a liberal. “I want lower taxes; I want less regulation,” he told Colbert, highlighting traditional Republican principles that he maintains.

Scarborough is, however, forfeiting his status as a top dissenting voice within the president's party. That's a big deal.

Here's an example that illustrates the significance:

On an episode of “Morning Joe” last August, Scarborough interrupted Brzezinski as she slammed congressional Republicans for refusing to reject their presidential nominee.

“Mika, you’re a Democrat,” he said. “Let me say this. Let me say this because it means nothing coming from you. You’re a Democrat.”

“Excuse me?” Brzezinski replied.

“It means nothing coming from a Democrat to these Republicans,” Scarborough continued. “Let me say this to my Republican Party: You are letting Donald Trump destroy the party.”

Scarborough won't be able to say things like that anymore.

His decision seems to cede that the Republican Party is now the party of Trump. Only a short time ago, Republicanism and Trumpism seemed like different canons. At the Conservative Political Action Conference in February, Trump said that he skipped last year's gathering because “I was worried that I would be, at that time, too controversial.”

Now, however, Republicanism is Trumpism — for many voters and politicians, anyway.

On a surface level, Scarborough's exit from the GOP would appear to upend the fundamental conceit of “Morning Joe” — two strong-willed hosts, one Republican and one Democrat, bantering about the news. But in practical terms, it probably won't alter much. Scarborough and Brzezinski have been in sync on Trump, and his views on other issues appear unchanged.