Story highlights Earlier Thursday, Kasich's super PAC began to air a spot portraying Trump as ill fit to be commander in chief

The super PAC supporting John Kasich, New Day for America, will spend millions against Trump in New Hampshire

Washington (CNN) Donald Trump unleashed a barrage of negative tweets against John Kasich Thursday night after the super PAC supporting the Ohio governor announced it would levy $2.5 million in attack ads against the real estate mogul.

The super PAC supporting Kasich, New Day for America, will spend the millions against Trump in New Hampshire, a state where Trump holds a stubborn double-digit lead and where Kasich has focused his campaign. The salvo began earlier Thursday when the Kasich group began to air a spot portraying Trump as ill fit to be commander in chief

The Kasich group's buy is the most aggressive yet to counter Trump's positioning in the Granite State and elicited a tough response from the GOP front-runner in the form of a dozen tweets -- one of which included a threat to sue over the ads.

"I want to do negative ads on John Kasich, but he is so irrelevant to the race that I don't want to waste my money," read one of Trump's tweets.

I want to do negative ads on John Kasich, but he is so irrelevant to the race that I don't want to waste my money. — Donald J. Trump (@realDonaldTrump) November 20, 2015

"Watch Kasich squirm --- if he is not truthful in his negative ads I will sue him just for fun!" read another.