 -- Democratic vice presidential nominee Sen. Tim Kaine attacked Donald Trump as a danger to national security for his seeming to encourage Russia to hack Hillary Clinton's emails, and sought to compare the Republican nominee's remarks to the Watergate scandal that led to the resignation of President Richard Nixon.

"A president was impeached and had to resign over an attack on the DNC during the presidential election in 1972. This is serious business," Kaine said on ABC's "This Week," referring to a hack this summer of the Democratic National Committee's computer systems, which federal security officials believe may have been done by individuals linked to Russian intelligence services.

Trump "has openly encouraged Russia to engage in cyberhacking to try to find more emails or materials, and we know that this cyberattack on the DNC was likely done by Russia," Kaine told ABC's Martha Raddatz.

He was referring to Trump's comment at a news conference in July about missing emails of Clinton's: “I will tell you this, Russia: If you’re listening, I hope you’re able to find the 30,000 emails that are missing,” Trump said.

The Democratic vice presidential hopeful called the comment "an attack that is being encouraged by Donald Trump on the DNC by Russia, similar to what led to the resignation of a president 30 years ago."

Kaine also defended Clinton's use of a private email server during her time as secretary of state.

The vice presidential nominee said his running mate welcomed the FBI releasing the notes from its investigation into classified information on the server.

"The reason these materials are being made public is that Hillary Clinton said I want the public to see them," Kaine said. "When Congress asked the FBI, 'Give us your notes,' Hillary said yes, that’s great. Give them your notes but let the American public see it."

The FBI said in a statement accompanying the release that it was doing so "in the interest of transparency and in response to numerous Freedom of Information Act (FOIA) requests."

FBI Director James Comey recommended in early July that Clinton not be indicted based on the bureau's investigation. The notes and other documents "demonstrate clearly why the FBI saw no need for additional criminal proceedings," Kaine argued.

Clinton "did make a mistake and she made [it] by deciding she wanted to use one device rather than multiple devices. She’s apologized for that. She said it was a mistake. And she’s learned from it," Kaine said.

Kaine also responded to criticism that his running mate has not held a formal press conference in 274 days. He turned the tables and hit Trump and his campaign for their treatment of the press.

“We’re not a campaign that is acting like Putin and other dictators and banning press outlets from even attending public events. That’s not American, but that’s what Donald Trump is doing,” Kaine said.

Asked when the public can expect Hillary Clinton to hold a press conference, Kaine said, “there’s been one in the last month.”

Kaine was referring to Clinton taking questions at a national convention for black and Hispanic journalists in August. But many in the media have argued this should not be considered a press conference because participants were limited and only three pre-selected reporters were allowed to ask questions.

“The questioners were limited to a small pool of convention participants, leaving most of the Clinton campaign press corps -- the dozens of journalists who know the campaign the best and who had complained the most about lack of access -- without an equal shot at asking a question,” wrote the fact-checking site Politifact.

Clinton’s last formal news conference was on Dec. 4. Kaine has held informal gatherings with his press corps to take questions four times since he became the vice presidential nominee in late July.