Rep. John Shadegg (R-Ariz.) announced late Monday that he will retire upon the conclusion of his current term, saying it was time for a new professional challenge.

Shadegg, anticipating attacks from Democrats claiming that he was vacating his seat to avoid a bruising campaign and potential loss to attorney Bob Lord (D), said there is no doubt in his mind he would have won an eighth term in November. Shadegg’s chief of staff, Sean Noble, is considered a leading candidate to succeed the Congressman, according to Republican sources.

“The bottom line is that this is a personal decision between my family and me, about our dreams, goals, and ambitions,” the 58-year-old Congressman said in a lengthy statement released Monday evening, “and we have concluded that it is time for me to seek a new challenge in a different venue to advance the cause of freedom.”

Shadegg added that his health is great, and he noted that his 2007 fundraising totals were among the best in his career. The Arizona Republican raised more than $1 million in 2007, to close the year with $864,000 in the bank. Lord finished 2007 with $503,000 on hand.

What Shadegg didn’t say in his statement was that two losing campaigns for positions in the House Republican Conference leadership could have affected his desire to remain in Congress. Shadegg lost his bid for Minority Whip to Rep. Roy Blunt (Mo.) following the November 2006 elections, and he lost a bid for Majority Leader to Rep. John Boehner (Ohio) earlier that year.

Democrats, who already saw an opening in Shadegg’s GOP-leaning, suburban Phoenix 3rd district, could be more enticed to go after the seat now that it is open. Although the district gave President Bush 58 percent of the vote in 2004, the Democratic Congressional Campaign Committee had already placed Shadegg on its list of top 40 targets.

“The Republican exodus from the House has reached historic levels, lending yet another major blow to national Republicans already demoralized and in disarray,” DCCC spokesman Doug Thornell said. “Shadegg, like 28 other Republicans before him, saw the writing on the wall. Bob Lord is already aggressively running and will turn this seat blue.”

Shadegg, a former leader of the House GOP’s caucus of conservatives known as the Republican Study Committee, was elected in the 1994 wave that saw the GOP take control of the House for the first time in 40 years.

His father, Stephen Shadegg, was a speechwriter and campaign manager to the late Sen. Barry Goldwater (R-Ariz.), one of the founders of modern conservatism.