Two self-styled progressives who had campaigned for higher office promising reform — if not a political revolution — met for the first time Friday in Philadelphia.

U.S. Sen. Bernie Sanders (Ind., Vt.), who ran in the Democratic primary for president, and Philadelphia District Attorney Larry Krasner, who was sworn into office in January, sat side by side in a Center City television studio, participating in a panel discussion that centered on criminal justice reform but also touched on the similar political forces that propelled both men into the national spotlight.

The appearance before a studio audience — the first time the political firebrands have appeared together — was the first in a series of events around the region this weekend for Sanders, who challenged Hillary Clinton for the 2016 presidential nomination and attracted attention for proposals including a $15 minimum wage and universal health care.

Sanders also spoke Friday night at a City Hall rally for John Fetterman, a Democratic candidate for lieutenant governor, where a protester with a bullhorn climbed onto the stage and berated the senator.

The man, wearing a white T-shirt, black bandanna, and sunglasses, approached within 6 feet of Sanders and shouted something about Russia. He was on stage for at least 30 seconds before Philadelphia police apprehended him after a brief struggle.

Police officials said Friday night they were unable to provide any information on the suspect.

Sanders was scheduled to appear Saturday with two Democratic congressional candidates in Allentown.

Although Sanders had expressed support for Krasner during the district attorney's race — and Krasner did not shy away from comparisons to the senator — Krasner's office said the two men had not previously met despite their shared appeal among left-leaning voters.

The panel discussion also featured Premal Dharia, director of litigation at Civil Rights Corps, an advocacy group, and Keeanga-Yamahtta Taylor. It was moderated by journalist Daniel Denvir and broadcast live on Facebook.

The talk centered on familiar themes for Krasner: making changes to cash bail, sentencing recommendations, and specifying the cost of incarceration. Sanders was complimentary of those efforts, saying they constituted the beginning of a national wave to bring about change to a system that all panelists described as broken.

"We have a broken criminal justice system that is begging, begging for real reform," Sanders said. "And the good news [is] … we are seeing here in Philadelphia, and all around the country, the beginning of an effort to bring about significant reform."

Staff writer Tom Avril and staff photographer Elizabeth Robertson contributed to this article.