The former president touted his wife's accomplishments as President Barack Obama's first secretary of state -- starting with sanctions against Iran -- as he lashed out at Trump for calling his wife's four-year tenure a failure in an interview with CNN's Erin Burnett.
"Well the thing about branding is, you don't have to be -- you can be fact-free," Clinton said with a smile, drawing laughs from a crowd of dozens that watched the interview.
It was a rebuttal to comments Trump made in a Monday interview with Burnett about Hillary Clinton, the Democratic presidential front-runner.
"When we look at the job that Hillary did as secretary of state, she goes down as perhaps the worst secretary of state in history," Trump said then.
Bill Clinton pointed to his wife's efforts to impose sanctions -- getting Russia and China on board -- that precipitated negotiations over the Iran nuclear deal. He said that while that deal has proven controversial, the sanctions were roundly considered a success.
"Even the Republicans admit that the sanctions on Iran were well done," he said.
"And that was a major achievement, to get Russia and China to agree to sign off on these sanctions and enforce them," he said. "She did that. That's what made the talks possible, so even the people who don't like the Iran deal, like the sanctions."
He also highlighted her work on the new START treaty with Russia, saying that "having these two sides still committed to reducing the number of nuclear warheads and missiles, I think, is a good thing."
He said Hillary Clinton's efforts to expand the number of beneficiaries from the George W. Bush-era anti-AIDS program known as the "President's Emergency Plan for AIDS Relief," or PEPFAR, from 1.7 million people to 5.1 million by using more generic medicines.
"These are all facts, so they're not common to the diatribe here," Bill Clinton said.
And he said Trump's criticisms of Hillary Clinton would be ripped apart in the context of a general election.
"You know, if he becomes the nominee, he'll have to sort of hone his criticisms a little more finely because the facts will be easy to marshal," he said. "But you know, he's good at this, that's what he does. And the people that he is telling it to now basically have only heard that story, so they believe it and it's probably good politics for him."
That point was part of Clinton's broader criticism of political media. He blamed his wife's struggles in polls -- where voters have increasingly questioned her trustworthiness -- on a press that has picked up on Republican criticism over issues like her use of a private email server.
He said to Burnett: "If I were sitting in your chair and you were sitting here, and you wanted to run for office, and I had four or five months to make sure nothing but the opposition's negative claims on you were run, and I presume your guilt with every question, and I beat up on you, do you think I could run your favorables down?"
In another jab at Trump, Clinton said the GOP front-runner "told me what a good job (Hillary Clinton) did in the Senate for New York after 9/11."
He also said Trump will eventually need to offer more policy proposals of his own.
"You have to be able to brand yourself. You have to be able to be identified," Clinton said as he acknowledged he believes Trump has a chance to win the Republican nomination. "But at some point you also have to say what are you going to do. You can't just spend all your time saying everything everybody else did was wrong and they were all doofuses."
He also indicated -- without offering specifics, beyond that he'll likely participate in more fundraisers -- that his own role in the campaign might pick up now that the Clinton Global Initiative event in New York has wrapped up.
He said he'll "go talk to her supporters and tell them what I think they should know, and answer their questions, and free her up to campaign more. I have no idea what else I'll do."