Former Green Party presidential nominee Ralph Nader wouldn't commit to saying Hillary Clinton would be the Democratic standard-bearer in 2016, saying Wednesday on CSPAN that potential scandals could derail her bid.

Throughout his campaign, Nader, like Sen. Bernie Sanders (I., Vt.), criticized Clinton for her coziness with Wall Street, hitting her for the highly paid speeches she made before institutions like Goldman Sachs. Clinton has repeatedly refused to release the transcripts for those speeches, to the chagrin of many on the left in the Democratic Party.

Nader also mentioned "the email situation," a reference to the private email server she used as secretary of state that's been the subject of a lengthy federal investigation.

On CSPAN's Washington Journal, the host asked Nader who he thought would win the Democratic nomination after Sanders' victory in Indiana Tuesday that still left him far behind Clinton in the delegate count.

"We don't know what scandals may befall Hillary Clinton," Nader said. "You still have the email situation. You still have her refusal to disclose transcripts before closed-door business conventions that were paying her $5,000 a minute. That's still up in the air."

He said the "big story" of the presidential campaign had been the surprising success of Sanders, whose populist, socialist candidacy has pushed Clinton to the left on several issues.

"He's proved that you can raise a lot of money in small denominations," Nader said. "It challenges the myth that you have to go to big multi-millionaire funding parties and Super PACs, so he's already made a great contribution."

Nader has run for president five times, most notably in 2000 on the Green Party ticket.