Both Sanders and Kasich ran unsuccessful campaigns for president.
CNN anchor Jake Tapper moderated part of the panel and asked Kasich whether Trump's alleged actions could be considered an obstruction of justice.
Earlier in the town hall, Kasich made clear he wasn't there to defend Trump. CNN has not viewed the memo but sources described it to CNN.
Sanders has been calling for a special prosecutor to lead the investigation into the Trump administration's possible ties to Russian Federation, as well as for an independent FBI director who is not involved with the Trump administration, at least since Comey was sacked last week.
After speaking to Trump on February 14, Comey was so appalled by the request that he wanted to document it, sources told CNN.
In the official statement sent to Bustle, Sanders calls for four things he believes we need "now more than ever" - a special prosecutor for the Russian Federation investigation, public recordings from the Oval Office, an independent FBI director, and Republicans holding Trump accountable.
"I hope you can let this go", Comey wrote, quoting the President.
Bernie Sanders has become a popular critic of the new US President and there have been suggestions that the 75-year-old could have beaten Trump to the White House had he won the race to become the Democrat candidate for last year's election.
"Is Trump a liar, or am I using hyperbole here?"
"I think this is a sad day", said Sanders.
A retired social worker and his party's national spokesman on health and social care, Mr Sanders said he knows many people of his age who are waiting for hip and cataract operations and warned the NHS is in danger.
"The fact we are the only party that says we must put in the money that is needed and stop privatisation, I am very proud of that".
Still, Kasich argued that the current scandal is "a long way" from the same conclusion that resulted from the Watergate scandal with President Richard Nixon. "The things that have swirled around this White House are the reasons that caused me not to move forward and support him both in the primary and going to that Republican convention", he said. The Vermont senator, who has always been critical of Trump's words and actions during the presidency (and well before), spoke out to make several requests for the future.
"I think John is thinking about becoming a democratic socialist", Sanders quipped in a reference to his own political identification.
Kasich said Republicans shouldn't "hide" from the controversy, but also cautioned Democrats against exploiting the issue.