WASHINGTON - When Sen. Pat Toomey (R., Pa.) opened a speech to Pennsylvania political insiders in late April, he pointed to his record of bipartisan cooperation with Sen. Robert P. Casey (D., Pa.) in advancing judges nominated by President Obama.

But Democrats and their liberal allies accused Toomey this week of quietly creating trouble for a Philadelphia nominee he had publicly praised.

Toomey rejected the allegation, saying he still supported Luis Felipe Restrepo, a District Court judge, for a vacancy on the U.S. Court of Appeals for the Third Circuit, based in Philadelphia.

Democrats say Toomey is an obstructionist, helping Republicans block Obama at every turn. Toomey's allies say his opponents are inflating a procedural issue to score political points against a man they desperately want to unseat next year.

The scuffle is likely a preview of many months to come as Toomey faces a tough reelection campaign.

It hinges on a piece of paper: the so-called "blue slip."

By tradition, the Senate Judiciary Committee will not hold a confirmation hearing until it receives blessings - in the form of the slips - from a nominee's home-state senators.

Casey submitted his blue slip for Restrepo in November, the month he was nominated.

Toomey, despite lauding Restrepo, has not.

"Why doesn't he come here - the junior senator from Pennsylvania - to talk about this man being held up by his own party?" Senate Minority Leader Harry Reid (D., Nevada) said on the floor this week. "There is no reason that he's held up for six months other than the Republicans just simply want to do everything they can to create problems for President Obama."

Toomey and his aides have declined to publicly say why the senator has not turned in the blue slip.

Toomey said Thursday that he had not delayed Restrepo's nomination.

The Judiciary Committee is reviewing Restrepo's background and will not hold a confirmation hearing until that process is complete, regardless of the slip, Toomey said.

"I am supportive of Judge Restrepo, as I have said repeatedly, and I'm also confident that he will be confirmed, certainly this year, hopefully sooner rather than later," Toomey said. "There is nothing that I could have done at this point that would have Judge Restrepo in any different circumstances."

Toomey said his cooperation with Casey had enabled Pennsylvania to fill as many judicial vacancies as any state - and possibly more - during Obama's tenure.

A spokeswoman for Sen. Chuck Grassley (R., Iowa), the Judiciary Committee's chairman, confirmed that Restrepo's background check is ongoing.

"It's prudent for senators to not return the blue slip until the background investigation is completed to ensure that there are no concerns found," the spokeswoman, Beth Levine, wrote in an e-mail. "These are lifetime appointments, so the committee can't afford to be wrong."

Democrats say that they have already completed their review and that Restrepo's vetting should be straightforward; he underwent a full review less than two years ago and was confirmed to his District Court seat in June 2013.

Restrepo, a former civil rights lawyer in Philadelphia, was nominated to the appellate bench Nov. 12.

In a news release then, Toomey said Restrepo would "make a superb addition" to the court, which hears appeals of cases brought in Pennsylvania, New Jersey, Delaware, and the U.S. Virgin Islands.

A "significant majority" of the American Bar Association's Committee on the Federal Judiciary rated his as "well qualified" - its highest rating.

Casey spokesman John Rizzo said the Democrat was "hopeful and optimistic" Restrepo would soon be confirmed "on a bipartisan basis."

Liberal groups have hammered Toomey over the delay, noting that the vacancy has been labeled an emergency - a designation based on the size of the caseload when there is a vacancy. Restrepo would fill a seat that has been open since July 2013.

Paul Gordon, senior legislative counsel for the liberal-leaning People for the American Way, accused Republicans of holding vacancies open as long as possible, even if nominees are eventually confirmed.

"If you create a bottleneck" in the committee and on the slow-moving Senate floor, Gordon said, there will be more vacancies to fill when a new president - perhaps a Republican - takes office.

Four judicial nominees had confirmation hearings Wednesday. All were nominated the same day as Restrepo or later.

Levine said the committee had moved as fast as or faster than Democrats did in the final years of the Bush administration, a point that Democrats dispute.