Washington: With the US Presidential election 2016 in limelight, the restraint of former US President Bill Clinton finally broke on Sunday as he launched a sharp attack on Democratic presidential hopeful Senator Bernie Sanders, who is the main Democratic presidential rival of Clinton's wife, Hillary, thus far.

"Hillary's opponent has a different view," Clinton said, without mentioning Sanders by name. "It's a hermetically sealed box. It's very effective. The system is rigged against you by the big banks, and both parties are in the thrall of the big banks. Anybody who takes money from Goldman Sachs couldn't possibly be president."

Clinton got animated while referencing to a report about how Sanders has been a prolific fundraiser for the Democratic Party - meaning the Senator has good relations with the rich people, including some in the financial sector, he keeps on slamming.

Clinton said he "fell out of [his] chair" after reading the story, joking that Sanders "may have to tweak that answer a little bit, or we may have to get a write-in candidate."

Hillary Clinton has also increased her criticism of Sanders, accusing the Senator of engaging in "artful smears" against her. But no one from Hillary's campaign had targeted Sanders so openly until Sunday. Bill Clinton was also quite restrained while campaigning last week in Iowa but on Sunday the former president accused Sanders' supporters of being sexist and attacking his wife's backers online.

"[Those] who have gone online to defend Hillary and explain why they're supporting her have been subject to vicious trolling and attacks," Clinton said, calling the comments "profane" and "sexist."

Sanders denounced these so-called "Bernie bros" earlier Sunday in an interview. "Look, we don't want that crap," he said. "Anybody who is supporting me that is doing the sexist things is - we don't want them. I don't want them. That is not what this campaign is about."