He liked her so little he got on the ballot as an independent in her race this year. And she lost. (Democrat Maggie Hassan won.)
But did Day really beat her?
"Beating Ayotte was my goal," Day says, in a phone interview this week. "I appeared in a Breitbart article in November of last year in which I threatened to get in [the race] over Medicaid expansion" which Ayotte supported.
Day has been all about trying to beat Obamacare and Medicaid expansion, and launched a SuperPAC that tried to make sure only Republicans who shared that goal survived.
"If the New Hampshire GOP isn't for getting rid of Obamacare in its various forms, we have no Party," he says. (Day says that, with his independent run done and no further plans for any running for office himself, he's a Republican again.)
Given that he earned 17,742 votes and Ayotte lost by just over 1,000, Day thinks he was the secret ingredient that brought her down.
But some have done fine-grained vote analysis that makes it seem more likely that a Day voter, minus Day, would have voted for the Libertarian Party's Senate pick, Brian Chabot.
As quoted in the Union-Leader, Kathy Sullivan, a Democratic National Committeewoman from Manchester, noted that Libertarian candidates in the state tended to get around 30,000 votes, including Gary Johnson for president and Max Abramson for governor.
And if you combine Day's 17,742 with Chabot's reported 12,597, you get right around the typical total L.P. vote in the state.
Certainly if you combine the two "liberty movement" candidates and their approximately 30,000 votes and presume that even 4 percent of those voters would have, absent their presence, voted for Republican Ayotte, the liberty movement writ large in the state can be credited/blamed for costing the GOP a precious Senate seat.
Day thinks it's "completely untrue" to say that he was in direct competition for votes with Libertarian Brian Chabot, who he writes off as a "left-libertarian" who believed in single-payer health care, the very opposite of Day's stance.
Day thinks he has some empirical evidence to back his claim that he was pulling more votes from otherwise Republican voters than otherwise Libertarian ones.
"I am involved in two different election recounts" in New Hampshire races, he says, and in the (unscientific) sample of ballots he's gotten to review in the course of them, "85 percent were straight GOP tickets with me as the only outlier."
"This was one of the most expensive state races in the country," Day says, with $30 million spent. "The question is, why did I get 17 thousand votes, given that I didn't spend any money, had no campaign website, didn't go to debates, didn't give speeches, and didn't have yard signs? How did I get five thousand more votes than the Libertarian? It's because the hardcore Republicans and the liberty community and the Free Staters see my name on the ballot and know who I am."
Day has another reason for being confident he shifted votes that would have been Ayotte's, though he stresses "I'll probably be blamed for this but I had nothing to do with it": three mailers sent to Republican voters in the state, with no identifying sponsor in violation of campaign finance laws, that hyped Day as better than Ayotte in right-wing terms on Obamacare, the environment, and guns.
Among Day's other complaints against Ayotte are that she, from Day's perspective, helped cost the state its speaker of the House Bill O'Brien, who he admires and supports. As far as he's concerned, with Ayotte, "every vote is the wrong vote," including voting to confirm Loretta Lynch as attorney general.
Day points to her Heritage Action rating of just 26 percent, compared to a GOP Senate average of 57, as another sign of why Ayotte had to go. Day also thinks her past record as New Hampshire's attorney general was rife with corruption, including declining to prosecute what Day calls a Ponzi Scheme.
Day tried to get former gubernatorial candidate Andrew Hemingway to run as an independent against Ayotte, but when Hemingway declined Day stepped in himself. "I was my own last choice," Day says. He accuses the state GOP of an "unprecedented" legal attempt to disqualify his ballot petitions, saying they knew from the beginning he could be what ruined her.
"Any state Republican Party leader who is angry with me about [Ayotte losing] will all be voted out" of their leadership positions, Day confidently predicts. "I don't care to talk to the current leadership in the New Hampshire GOP. I'll just wait until they are replaced."
Day does not relish have to support primary challenges to Republicans he sees as weak, or spend his time on "wacky independent runs to take out Ayotte. That's not my goal. But I'm the only one sometimes" willing to do what he thinks is necessary to make the Republican Party a party of liberty.
"I'd like to be able to work cooperatively with a Republican majority on things like school choice, repealing Obamacare, decriminalizing marijuana," and helping elect candidates on the town council and school board level to rein in state property taxes which he thinks are "out of control."
"I want to go into a more constructive phase. I never want to have to do what I just did" again, Day says. The GOP probably is with him on that.