(CNN) Sen. Jeff Flake tweeted a picture Tuesday afternoon that is the most visible sign yet that his break from the Trump-led Republican Party may not only be permanent but also could lead to a national bid for the Arizona Republican down the line:

The check is made out to Doug Jones, the Democratic nominee against Roy Moore in next Tuesday's Alabama special election to fill the Senate seat of now Attorney General Jeff Sessions. And it carries the now-familiar refrain of the anti-Trump wing of the GOP: "County over party."

Flake's decision to cut a check to the Democrat Jones comes 24 hours after President Donald Trump formally endorsed Moore's candidacy -- despite the fact that the Alabama Republican faces charges of pursuing inappropriate relationships with teenage girls when he was in his 30s.

It also comes hard on the heels of the Republican National Committee's decision to reinvest in the Alabama race just weeks after pulling out following the bevy of accusations against Moore.

What is Flake up to?

On the one hand, he undoubtedly believes that Moore -- given the allegations against him -- should not be in the Senate.

On the other, Flake's decision to write a check to Moore's Democratic opponent -- coupled with his book published this spring in which he blasts the Republican Party for accepting Trump into its ranks and his willingness to repeatedly hammer away at the President over the past 10 months -- suggest that the Arizona senator may have his eye on a third-party presidential bid in 2020.

And Flake's answers on whether he might run in 2020 have been very cagey. Check out this back-and-forth with CNN's Jake Tapper on the day Flake announced he wasn't running for reelection to the Senate earlier this fall:

TAPPER: "(Should) somebody in the Republican Party, perhaps you, should challenge the President in 2020?"

FLAKE: "I won't go there. That's a long time away."

TAPPER: "So, you're not -- you're not discounting it?"

FLAKE: "Certainly, I didn't support the President in the last election, and -- but it's early. That time will take care of itself."

Which is, um, not a "no." And if you did want to run a third-party party bid for president in 2020, casting yourself as a conscientious objector to Trumpism and a voice for "country over party" isn't a bad place to be.

The Point: Flake isn't actively planning to run for president. But he's doing things -- like releasing the fact that he wrote a check to Moore's opponent -- that he knows will draw attention to him and raise his profile as a Trump rejectionist. That's not by accident.