Republicans in the Senate will gain one more voice against repeal of “Don't Ask, Don't Tell” with Monday's swearing in of Mark Kirk.

The Illinois Representative will serve the remaining weeks of President Barack Obama's unexpired term. Democratic Senator Roland Burris was appointed to the seat after Obama became president but didn't run for the post. Kirk's full term begins in January.

Burris supports repeal of the policy that bans gay and bisexual troops from serving openly. But as a representative, Kirk voted against a measure that would repeal the gay ban.

That vote cost Kirk the endorsement of the Human Rights Campaign (HRC), the nation's largest gay rights advocate, which had endorsed the five-term congressman over an openly gay Democrat in 2004. HRC instead backed pro-gay marriage Illinois Treasurer Alexi Giannoulias.

A Senate committee will hold two days worth of hearings on a Pentagon report on repeal of the law this week before the measure moves to the Senate floor.

The addition of Kirk, who is expected to oppose repeal, increases the likelihood that Senate Republicans will block the measure for a second a time.