Massachusetts Rep. Barney Frank says in a new ad that Mitt Romney has “no principles” when it comes to gay rights.

The 72-year-old Frank has the distinction of being the first congressman to voluntarily come out gay and the first sitting member of Congress to enter into a marriage with a member of the same sex. He retired from Congress this year and won't return next year.

“It is clear, if you want to sum up his evolution on LGBT rights, 'Mitt gets worse' is a very accurate phrase,” Frank says in the 5-minute video released Thursday by the Mitt Gets Worse campaign.

Frank says Romney has been “especially inconsistent” on LGBT rights.

After noting that Romney said in 1994 that he would be “better on LGBT rights than [Senator] Ted Kennedy,” he then adds: “He has never been in favor of any legislation or executive order that would advance our rights. Zero. None.”

“This is a man who has no principles on this subject. How do you go from saying I'll be a better advocate than Ted Kennedy to not even endorsing an anti-discrimination in employment law? He will get as bad as he has to be for political advantage,” Frank says. (The video is embedded on this page. Visit our video library for more videos.)

(Related: Mitt Romney's gay rights record targeted in Mitt Gets Worse campaign.)