Republican Sen. Scott Brown of Massachusetts called "standing with President Obama" a great experience in a radio ad posted to YouTube on Tuesday.

In the ad, part of an effort to tout his efforts at bipartisan compromise, Brown talks about his bill to help unemployed veterans. Congress passed the bill in November 2011 in a rare moment of agreement between Democrats and Republicans.

"A bill I introduced to give a tax credit to businesses that hire veterans was passed with bipartisan support," Brown says in the ad. "Standing with President Obama on the day he signed it into law was another one of those great experiences."

Brown was elected to replace the late Sen. Ted Kennedy (D-Mass.) in 2010 in an upset over Democrat Martha Coakley, and is the first Republican since 1972 elected to the U.S. Senate from the heavily blue state. This year he faces a challenge from progressive favorite Elizabeth Warren.

Now, while trying to hang on to that seat, Brown appeared at two signing ceremonies with President Barack Obama in April.

Brown's efforts to paint himself as a centrist may be working: As of early April he was tied with Warren in a Boston Globe poll.

Brown raised $3.4 million in the first quarter of 2012 versus Warren's $6.9 million, but he started with about $4 million more in the bank than she did.