Kaine was in full attack-dog mode during a series of television interviews, mocking Trump's high-profile meeting with Mexican President Enrique Peña Nieto on CNN's "New Day." He also criticized Trump for giving a more moderate immigration message to the Mexican leader, before delivering a fiery speech hours later to an American audience.
"Donald Trump did a kind of photo op fly-by, where he didn't even have the nerve at the last minute to bring up this issue about the wall," Kaine told CNN's Chris Cuomo. "This is the central piece of his campaign -- immigration and deportation, and we're going to build a wall and make Mexico pay for it. But when he looked President Peña Nieto in the eye, he couldn't even bring that up."
Trump said Wednesday that the payment for the proposed border wall didn't come up during his meeting with Peña Nieto, but the Mexican president disputed that assertion.
"That was a choke, and I think it shows that diplomacy is not for amateurs. Donald Trump's an amateur," he added.
"But isn't diplomacy about the soft sell?" Cuomo asked.
Kaine saId: "I think diplomacy is primarily about honesty and candor, and standing up for the values that you believe in. So Donald Trump's been saying for months, we're going to build a wall and Mexico's going to pay for it -- if he really believed that, when he was sitting down with President Peña Nieto, why not even bring that up? Then he goes back, and then to the hometown audience, he gives this fiery speech, language of division, you know?"
Kaine also said that Clinton would pursue immigration reform "in the first 100 days of the administration," modeled after the "pillars" of the Senate's 2013 attempt at immigration reform with the "Gang of Eight" bill.
The Virginia senator also hit Trump for his plan to target sanctuary cities.
"When Donald Trump kind of goes after these phantom sanctuary cities and talks about how bad they are, basically what he's going after is police chiefs," he said.
Citing his experience with the issue as a former mayor and governor in Virginia, Kaine said that local law enforcement explained to him that "if the immigrant community starts to see us as immigration officials, they won't call and complain about crimes in their neighborhood, they won't be witnesses in cases."
Kaine argued that "instead what you need to do is work with the community to protect and serve them, and let (Immigration and Customs Enforcement) do their job."
Kaine also responded to criticism that the Clinton campaign has been inaccessible to the press -- symbolized by the campaigns ongoing refusal to hold a press conference,
a trend that has continued for 271 straight days.
The Virginia senator pointed to Clinton's appearance at a press event with the National Association of Black Journalists and the National Association of Hispanic Journalists as an example of a press conference, and argued that the campaign "talks to the press every day."