By Rachel Kapochunas, CQ Staff

Arkansas Democrat Mark Pryor ’s bid for a second Senate term soared from highly likely to virtually certain Monday, when no Republican challenger met the state’s congressional filing deadline at noon central time.

CQ Politics has changed its rating on Pryor’s race to Safe Democrat from Democrat Favored, reflecting the fact that he is the first Senate incumbent running this year to officially draw no major-party opponent.

It was likely that this rating change would have been made even if the GOP had fielded a candidate. Republicans’ hopes for seriously competing faded after Asa Hutchinson, a former House member and former high-ranking official at the federal Department of Homeland Security, declined a Senate bid. Then former Gov. Mike Huckabee stuck to his pledge not to run for the Senate this year, even though he dropped his presidential campaign last week after Arizona Sen. John McCain won enough delegates to clinch the Republican nomination.

The GOP’s chances of even fielding a candidate fell to Tom Formicola, a medical technology company manager and former city councilman, who publicly considered the race but ultimately did not file to run, according to the office of Arkansas’ Secretary of State. Formicola’s only congressional campaign experience was a failed 2006 bid to win the GOP nomination to run against 2nd District Democratic Rep. Vic Snyder .

Still, the Republicans’ inability to field any Senate candidate in a Southern state that twice favored Republican George W. Bush for president this decade is yet another blow for a party that lost six seats and its Senate majority in 2006, and is mainly playing defense against further Democratic gains this year.

Having missed the filing deadline, any Republican who might belatedly decide to run against Pryor would have to do so as a write-in candidate.

The 45-year-old Pryor reported raising more than $4 million for his campaign treasury through the end of 2007 and had $3.6 million cash on hand. But as the prospect of a serious Republican challenge faded, Pryor was seen as piling up money more to protect against a rumored Democratic primary challenge from Lt. Gov. Bill Halter. That contest also failed to develop. Though Halter appeared to hedge last year by saying he had no “plans” to run against Pryor, he has been heavily focused on his effort to bring a lottery to Arkansas and never entered the Senate race.

Pryor’s clear path to re-election contrasts with the battle he had to wage to first win the seat in 2002, when he unseated one-term Republican incumbent Tim Hutchinson (the brother of Asa Hutchinson) by 54 percent to 46 percent. Pryor benefited that year from his image as a conservative-leaning Democrat, and the well-recognized name he inherited from his father, David Pryor, a popular figure who served the state as governor from 1975 to 1979 and as senator from 1979 to 1997. Mark Pryor ’s ability to maintain a center-right profile over his Senate term helped him secure his position in Arkansas, one of the few Southern states where Democrats maintain a strong foothold.

Pryor becomes the first senator to draw no opponent from the other major party since 2006, when Indiana Republican Richard G. Lugar enjoyed a free ride in his campaign for a sixth term. Idaho Republican Michael D. Crapo ran unopposed for a second term in 2004. Four senators ran opposed in 2002: Massachusetts Democrat John Kerry (fourth term); Virginia Republican John W. Warner (fifth term); Mississippi Republican Thad Cochran (fifth term); and Kansas Republican Pat Roberts (second term).

Bob Benenson and Greg Giroux contributed to this story.