Citizens United Political Victory Fund – run by longtime activist Dave Bossie — to hit Fox News Channel Thursday with six-figure television buy comparing McCain to Hillary Clinton.

McCain “joined Ted Kennedy to sponsor amnesty for illegals… John McCain — surprisingly liberal.”

Watch it above.

Could be the start of major conservative effort trying to stop McCain in favor of Romney.

Plus: Romney appears to be the favorite of conservative talk-radio stars and stands to benefit from their distaste for the Arizona senator.