DENVER -- The nominee for U.S. attorney withdrew her name Monday because of a political controversy about whether she violated the law in helping Gov. Bill Ritter get elected.

Stephanie Villafuerte said the controversy overshadowed her qualifications to become the top federal prosecutor for the region.

"Unfortunately, a needless and extraneous political fight has emerged in Colorado and that fight, in my judgment, has completely overshadowed the deliberative and independent assessment of my qualifications for this important office," she wrote President Barack Obama and Attorney General Eric Holder.

Villafuerte became subject to scrutiny over calls she made to the Denver District Attorney's Office, where she used to work under Ritter, about a Republican commercial questioning Ritter's record. The commercial blamed Ritter for allowing an illegal immigrant to plea to a lesser offense, before he committed a violent crime in California under another name.

An immigration agent in Colorado was fired for accessing a restricted law enforcement database to verify the illegal immigrant was the same person, and he faced federal prosecution but was acquitted.

Some Republicans have charged that Villafuerte urged her former colleagues to access the same database but she was never charged. She has denied asking for the restricted information.

In her letter, Villafuerte said she answered all the questions honestly and did nothing wrong.

"I continue to stand by my statements and maintain that my involvement was appropriate at all times," she wrote.

U.S. Sen. Mark Udall, D-Colo., asked that a new candidate be quickly considered.

"It's important now for the White House to move quickly to nominate a new U.S. Attorney candidate," Udall said in a written statement. "I will encourage the White House to look at the list of names that former Senator Salazar and I sent to the President in January."