Aside from holding up legislation and nominations, Senate Republicans likely have few other options to undo or retaliate against President Barack Obama’s recess appointment of Richard Cordray to head the Consumer Financial Protection Bureau, Senate GOP aides said today.

“We’ll see what shakes out when [Members] return,” an aide said.

Ostensibly lawmakers could look to slow progress on White House or other Democratic initiatives, though no members, to date, have announced that they plan to do so.

“It certainly doesn’t help relations,” another GOP aide said.

Republicans also said they expect that any legal challenge to Cordray’s installation would likely come from entities regulated by the CFPB, rather than from GOP Members. However, they said nothing has been ruled out.

Democrats charge that Republicans spent all last year obstructing their agenda, so there would be no appreciable difference from their current approach to working with Democrats.

“We are not concerned with retaliation,” a Senate Democratic aide said, adding that the GOP has not been a productive legislative partner.

Senate Republicans blocked nominations at the end of last year because the White House would not promise to hold off on any recess appointments. GOP Senators successfully waged filibusters against legislation 13 times in 2011.

Still, Obama’s move does not bode well for negotiations to extend an existing payroll tax cut through the end of the year, unemployment insurance and the Medicare physician fee fix. Both the House and Senate passed a two-month extension of those programs after a standoff over the length of the extension. Now, a conference committee has been charged with reconciling the deep differences between the chambers on a yearlong continuation of all three programs.

But the White House’s decision to interpret his recess appointment powers more broadly than other presidents have has created a procedural conundrum for the Senate.

Senate Republicans raised questions about the procedure in place to prevent recess appointments. Senate Majority Leader Harry Reid (D-Nev.) pioneered the use of pro forma sessions to keep Congress in session in order to keep President George W. Bush from making appointments while Congress was recessed.

Bush, however, never challenged the procedure as Obama did with the Cordray nomination today.

Traditionally, presidents have waited for more than a week after Congress has officially adjourned for recess before using their constitutional power to temporarily install a nominee in an administrative or judicial post. Some legal scholars have long argued the recess appointment power is vaguely outlined and allows presidents some wiggle room.

In this case, Congress was not even officially recessed because the chambers had not agreed to a formal adjournment resolution allowing both to be out of session for more than three days. That has forced the House and Senate to gavel themselves into session for pro forma sessions every three days. During those sessions, no legislative business is conducted.

A Senate Democratic aide said that Cordray’s nomination and the level of Republican obstruction warranted the challenge.

“This is a situation where Republicans have said on the record that they believe Mr. Cordray is qualified, and they’re blocking him just to extract concessions that will benefit their friends on Wall Street,” the aide said.

Sarah Binder, a historian of Congress at George Washington University and a senior fellow at the Brookings Institution, said in a blog post that she thinks it is probably a legal appointment.

“Although Republicans will likely challenge the appointment in court, it’s hard for me to see the Cordray appointment as more than an aggressive use of executive power in face of the opposition’s foot-dragging over confirming a nominee to the CFPB,” Binder said in a blog post. “The Constitution doesn’t define what constitutes a valid recess for the purpose of the president’s proper exercise of the recess appointment power, leaving it open to interpretation.”

She added that the White House also likely made the political calculation that there was more upside than downside for Democrats from the appointment, giving them another opportunity to position themselves as a friend of middle-class consumers and opposed to wealthy Wall Street banks.

“Certainly it fits the president’s electoral strategy of championing the rights of consumers as an advocate of the middle class and painting the GOP as a defender of dishonest financial lenders,” Binder continued.