Sen. John ThuneJohn ThuneCornyn: Knowing health plan ahead of vote is 'luxury we don't have' Sen. Thune: McCain ‘a hero' to ‘millions’ GOP signals infrastructure bill must wait MORE (R-S.D.), who passed on a 2012 presidential run Tuesday, said the "timing didn't feel right" for a run of his own next year, but said his decision doesn't close the door on a future White House run.  

"I felt if you're going to do this, you've got to do it," Thune told The Daily Republic of his decision not to make a bid for the Republican nomination next year. "I didn't want to do anything halfway."

In an interview after making his decision public Tuesday, Thune told the paper that he was conflicted over the past several months over whether to launch a campaign, waking up some days ready to declare his candidacy and other days wondering, "What am I thinking?"

But the South Dakota Republican said all future options are open, including the possibility of accepting a slot on the Republican ticket as vice president in 2012 or running in 2016, should President Obama win reelection. 

"That's a long ways down the road," he said. "The decision was, not now. I don't think it means not ever."

Despite encouragement on a 2012 run from several of Thune's Senate GOP colleagues, including Senate Minority Leader Mitch McConnellMitch McConnellOvernight Regulation: Trump administration reveals first regulatory agenda | GOP lawmakers introduce measures to repeal arbitration rule | Exxon gets M fine for sanctions violation Overnight Healthcare: CBO predicts 22M would lose coverage under Senate ObamaCare replacement OPINION | GOP healthcare attack is a vendetta against President Obama MORE (R-Ky.), Thune said his work is in the Senate, where his future could include a bid for GOP whip. Thune is  the No. 4 Republican in the upper chamber, serving as chairman of the Republican Policy Committee. 

The early read is that Thune's exit from the presidential field could aid a contender like former Minnesota Gov. Tim Pawlenty (R), who hails from the same region of the country and is likely to focus heavily on the Iowa caucuses if he jumps into the race.