U.S. Sen. David Vitter will campaign this weekend against his colleague in the Senate, Democrat Mary Landrieu.

Vitter will knock on doors in Baton Rouge Saturday morning with representatives of the national anti-abortion group, the Susan B. Anthony List.

University of Louisiana at Lafayette political science professor Pearson Cross says it's uncommon for a U.S. Senator to actively campaign against the other senator from his or her state.

"You don't really go after your colleagues in the Senate directly," Cross said. "You might support their opponents covertly, but in this case, there's no covert about it."

You might support their opponents covertly, but in this case, there's no covert about it

Landrieu is Catholic and has said she believes women should have the right to make their own decisions over whether to terminate their pregnancy. Cross says for many voters, a candidate's view on abortion helps them decide who to vote for.

"One of things about the abortion issue — for people to whom it makes a difference — it's the single issue that will decide their vote," Cross said.

Cross says it's also rare for a sitting U.S. senator to spend time knocking on the doors of voters' homes.

"Maybe in Wyoming, where you probably could meet all of the electorate over a six-year period," Cross said.