A week after the conservative Club for Growth launched a $1 million ad buy in Iowa slamming Republican presidential candidate Donald Trump’s conservative credentials, the Republican front-runner fired back Tuesday.  

In a scathing letter, Trump’s general counsel Alan Garten called the 16-year-old conservative organization a “pitiful little group,” said it “shamelessly attempted to extort Mr. Trump to the tune of $1 million” in exchange for its endorsement, and demanded that it remove its two ads from the air. The episode pits the Club for Growth, a group that typically supports candidates who are a thorn in the establishment’s side, against Trump, one of the greatest thorns the Republican Party’s establishment has felt. It’s also placed a politician who has been referred to as a bully – from derogatory comments about women such as Fox News anchor Megyn Kelly, entertainer Rosie O’Donnell and Republican presidential opponent Carly Fiorina, to remarks about Republican Sen. John McCain’s heroism in the military – in the position where he claims he is the one being bullied.

When I intelligently turned down The Club For Growth crazy request for $1,000,000, they got nasty.What a waste of money that would have been

— Donald J. Trump (@realDonaldTrump) September 2, 2015

Actually @realDonaldTrump asked for that mtg & then asked for races he could support. Thought he could buy us off. Worst Kind of Politician — CFG + CFG Action (@club4growth) September 2, 2015