Stephen K. Bannon, who was President Trump’s chief strategist, has garnered national attention after leaving the White House as he tries to influence political races, and is sometimes given equal billing with Mr. Trump in some news accounts about their different stands.

This week, Mr. Bannon has another platform to criticize the Republican establishment and to portray himself as defender of the movement that elected Mr. Trump.

Mr. Bannon returned on Tuesday to the Sirius XM radio show, an outlet with 32 million subscribers, that he had hosted before joining Mr. Trump’s campaign. The daily program provides an additional venue for the leader of the Breitbart News website to toss political grenades at people like Senator Mitch McConnell, the majority leader, as the 2018 midterm election cycle begins.

Mr. Bannon said in a statement that he had always planned to return to radio after he left the White House in August.