HELENA -- Bob Keenan, the top Republican leader in the Montana Senate, said Thursday he is considering challenging Sen. Conrad Burns in the primary election because he is "concerned'' about Burns' re-election chances because of a lobbying scandal.

"First, Republican voters need to make a decision about their gut-level support for Conrad,'' Keenan wrote in an e-mail from Costa Rica, where he is visiting his oldest daughter who is on a college exchange there. "If they are for Conrad, then vote for him in June and fight for him to win the November election. If they want an alternate, viable option they can be proud of, then for a high-quality, clean candidate named Bob Keenan.''

After the primary, Keenan urged Republicans "to unite for the winner.''

Keenan wrote later that he's not yet sure he's going to jump into the race. He, like others the Bigfork Republican has spoken with, is worried about Burns' race.

Keenan's statement came the day after the former Senate president and current Senate minority leader, confirmed he is not running for a seat in the state House of Representatives.

Term limits prohibited the leader from seeking another term in the Montana Senate.

Karl Ohs, chairman of the Montana Republican Party, said "the beauty of our system of government is that public service is honored and encouraged. Until Bob Keenan decides what he is going to do, I have nothing further to add.''

Ohs also praised Burns for his years in the senate and for helping to bring $2 billion in federal money to Montana.

Democrats, not surprisingly, had a different take.

"When Mr. Keenan returns from Costa Rica, we will welcome him with open arms to the large cross-section of Montanans who believe Conrad Burns' relationship with Jack Abramoff is both embarrassing and hurting Montana,'' said Matt McKenna, a spokesman of the Montana Democratic Party.

Burns has been consistently linked to the ongoing U.S. Justice Department investigation into lobbying abuses involving Jack Abramoff, who pleaded guilty in January to corruption related charges.

Burns received around $150,000 in campaign contributions from Abramoff, his associates and tribal clients more than any other lawmaker, according to the Washington Post.

That newspaper, and others, has reported that Burns is under investigation by the Justice Department. The paper has cited anonymous sources. Burns has consistently said no one from the agency has contacted his office about the investigation.