WASHINGTON — Representative Michele Bachmann, the Minnesota Republican whose status as a leading Tea Party voice in Congress has faded in the wake of a failed bid for president and a widening investigation into her campaign spending, said Wednesday that she would not seek re-election.

Mrs. Bachmann, defiant as ever as she insisted that she would have won re-election had she tried, said the legal inquiries had nothing to do with her decision. She vowed to continue to fight for the principles she said she holds dear: religious liberty, traditional marriage, family values and opposition to abortion.

“I fully anticipate the mainstream liberal media to put a detrimental spin on my decision not to seek a fifth term,” she said in a gauzy network-television quality video posted on her campaign Web site. “They always seemed to attempt to find a dishonest way to disparage me. But I take being the focus of their attention and disparagement as a true compliment of my public service effectiveness.”