On Tuesday, with the lead-off of six scheduled Democratic debates, voters will have their first chance to take the measure of the passionate newcomer to the national scene alongside front-runner Hillary Rodham Clinton.

For the former secretary of state, the debate stage is a familiar setting and one where she has performed well in her previous races for senator and for president. But it is also well-suited to Sanders, say his aides and those who have seen him square off against opponents in Vermont.

"He speaks from a certain kind of certainty, a declarative voice, steeped in a certain amount of outrage," said Greg Guma, a liberal activist and journalist in Vermont whom then-Gov. Madeleine Kunin recruited to play Sanders in debate rehearsals when the mayor of Burlington challenged her as an independent in 1986 (Sanders came in a distant third).