Veteran Washington Post reporter Bob Woodward on Monday compared the email controversy engulfing Democratic presidential candidate Hillary Clinton to the downfall of President Richard Nixon.

On MSNBC's "Morning Joe," Woodward, who through his reporting helped break open the Watergate scandal, said it's at least suspicious that Clinton's emails from her tenure as secretary of state were wiped away from a server she owned privately.

"Follow the trail here," Woodward said. "There are all these emails. Well, they were sent to someone or someone sent them to her. So, if things have been erased here, there's a way to go back to these emails or who received them from Hillary Clinton. So, you've got a massive amount of data in a way, reminds me of the Nixon tapes: Thousands of hours of secretly recorded conversations that Nixon thought were exclusively his."

News broke earlier this year that Clinton relied on a private email address and server, rather than a government-owned one, when she served at the State Department. Subsequent reports said that she received classified and top secret information through that system. Federal officials have since taken Clinton's server and are continuing an investigation into whether its security was compromised.

"It's extraordinary," Woodward said. "Again, it's the volume: 60,000 emails and Hillary Clinton has said 30,000 of them, half, were personal and they were deleted. Who decided that? What's on those emails? I would love to have all 60,000, read them. It would be a character study about her personal life and also what she did as secretary of state. And step back for a moment. The big question about Hillary Clinton is, who is she? Is she this secretive hidden person or is she this valiant public servant? Look at those 60,000 emails and you're going to get some answers."

Woodward added, "This has to go on a long long time; the answers are probably not going to be pretty."

Clinton maintains her status as the national front-runner for the Democratic presidential nomination, though her favorability ratings has declined since the news about her emails broke.