President Obama recently announced that he would hold a fiscal responsibility summit at the end of this month, with a particular focus on the long-term funding shortage that faces Social Security and Medicare.

And who's bound to be high on the guest list? None other than Sen. Judd Gregg (R-NH), who abruptly pulled out of contention to become Commerce Secretary today. Not to mention that when Obama releases his maiden budget proposal -- also likely to come before month's end -- the leader of the opposition will be none other than Gregg, the senior Republican on the Budget Committee.

All together now, everyone: Awkward!

"It really is going to be very interesting" when the budget debate pits Gregg against the Obama team, budget expert Robert Bixby told me. Bixby is executive director of the Concord Coalition, a nonprofit fiscal watchdog.

"I actually could never quite figure out why Gregg had accepted the Cabinet position in the first place, since it was obvious that [he and the president] had some very fundamental disagreements about fiscal policy," Bixby added.

The fact that Gregg spent less than 10 days as the Commerce Secretary-designate helps "mitigate the awkwardness," as Bixby put it, because it's unlikely that the GOP senator was sitting in on too many strategy meetings during his brief tenure as a Cabinet nominee.

But the unmistakable tension inherent in Gregg's sudden withdrawal is bound to resurface during budget season. Since almost the moment he arrived in the Senate 14 years ago, Gregg has been the go-to guy for Republican fiscal hawks. It's unlikely that he'll be able to avoid fierce confrontations over Obama's budget plan, especially if the president follows through on promises to assume the expiration of the tax cuts pushed through under Bush.

For the moment, however, the question is whether Gregg will "un-recuse" himself and return to Congress to vote on his almost-boss' stimulus bill. His spokeswoman did not return a request for comment on the issue.