Several Republicans have already announced, Roll Call reported. They include former Rep. Heather Wilson, who left the seat Heinrich now holds in 2008 to make an unsuccessful run for the Republican nomination for the Senate.
Heinrich announced his candidacy on Facebook and on his campaign Web site, saying he arrived at the decision after discussing "at length with my family how I might best continue to serve New Mexico."
"After much serious thought, I am excited to announce today that I will be a candidate for the United States Senate," he said.
With his entry into the race, Republicans have someone to be against, even if they are not yet unified on who to support.
"The contrast for voters will be very clear in 2012, and we are confident New Mexico will elect a fiscally responsible Republican to the U.S. Senate," Brian Walsh, a spokesman for the National Republican Senatorial Committee, said.
Bingaman, a Democrat, was first elected to the Senate in 1982.