Marco Rubio (R-FL) again denied interest in joining the GOP ticket, telling CNN Thursday he’s not going to be VP.

“My answer hasn’t changed on the vice presidential stuff. I know people keep asking me but my answer hasn’t changed,” Rubio told CNN one day after announcing his endorsement of GOP frontrunner Mitt Romney.

Asked whether the “under no circumstances” response that he gave earlier this year still applies, Rubio told CNN, “Yeah, I’m not going to be the vice president.”

Despite his denials, political observers in Washington largely believe the senator is playing coy.

“I think he might be asked [to be VP], but look, I think he’s got the right posture, which is it’s not seemly to go out there and say ‘I’m interested,’” Rove said on FOX News Thursday.  “I think he hit the exact, right tone, and look, you don’t want to be looking like you’re campaigning for something over which you have no control.”

Observers also point to recent evidence his team is gearing up for a national campaign. Rubio’s PAC paid $40,000 for investigators to research negative attacks that could surface against him.  He also recently asked the Florida Commission on Ethics to close a complaint filed against him during his 2010 campaign, which alleges he misused Republican campaign money for personal expenses. Rubio wrote to the commission and requested they resolve the matter quickly, noting that as long as it remains open, his opponents can claim he’s under investigation.

“This complaint was filed for political reasons, and those who support the direction this president is taking our country will undoubtedly attempt to exploit it for political reasons,” Rubio wrote in the letter.

With Rubio ending his neutrality in the GOP race and actively courting press, Democrats are stepping up their attacks on the freshman senator.  In a conference call Thursday with reporters, Florida state Rep. Darren Soto depicted Rubio and Romney as “increasingly out of touch” with Florida voters.

“I, for one, am not surprised to see Rubio turn his back on those who need it most because he has repeatedly turned his back on just about everyone much like Mitt Romney,” Soto said on the call.

Tags | Darren Soto, Karl Rove, marco rubio, Mitt Romney