Kansas Senator Sam Brownback argues he's the true conservative in the race for the 2008 Republican presidential nomination, not Massachusetts Governor Mitt Romney.

Brownback tells the Christian Broadcasting Network that Romney may have trouble explaining flip-flops in his background.

For example, Romney ran for governor in 2002 touting his support for abortion rights; now he highlights his opposition to abortion.

Brownback said that he -- not Romney -- is ``the solidly pro-life candidate.''

Social conservatives also point out that Romney said in 1994 that he'd be a better activist for the gay agenda than his then-opponent, Democratic Senator Edward Kennedy. Romney now touts his opposition to gay marriage.

A Romney spokesman said that as governor, Romney was ``a champion of traditional marriage.''