Mayor Brandon Johnson arrived in Washington, D.C. on Sunday ahead of a Congressional hearing Democrats expect will be light on policy and heavy on political theater.

Johnson, who will testify about the city’s sanctuary city status before a Republican-led House committee, has been preparing for the hearing by conducting mock hearings with members of his staff and speaking with top elected officials.

"He called me personally and asked what he can expect, and I told him it would be a trial by fire," U.S. Sen. Dick Durbin told NBC Chicago.

As first reported by the Chicago Sun-Times, the mayor's office hired a law firm in D.C. that helps prep witnesses to testify before Congress.

Johnson brought six members of his staff to D.C. They include: Senior Aide Jason Lee, Communications Director Erin Connelly, Corporation Counsel Mary Richardson-Lowry, Deputy Corporation Counsel Andrew Worseck, Deputy Mayor of Community Safety Garien Gatewood and Chief External Affairs Officer Kennedy Bartley.

During mock hearings, his staff members have played the Republican lawmakers who are on the committee.

The House Oversight and Government Reform Committee will hold the hearing at 9 a.m. CT Wednesday. The mayors of New York, Boston and Denver will also be questioned about sanctuary policies in their cities.

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The committee's chairman, Kentucky Republican U.S. Rep. James Comer, has said states and cities that do not comply with federal immigration agents should not receive federal funding. Chicago and Illinois both have laws on the books that limit local police officers' ability to cooperate with U.S. Immigration and Customs Enforcement, laws which have become the subject of a lawsuit from the U.S. Justice Department recently.

“The House Oversight Committee will hold sanctuary mayors publicly accountable for refusing to abide by the law and placing Americans’ lives at risk," Comer said in a statement.

Johnson has also contacted other Illinois leaders for advice, including former Mayor Lori Lightfoot, former education secretary Arne Duncan and former Mayor Rahm Emanuel. Emanuel told NBC Chicago that he told Johnson to remind Congress members that they have not passed comprehensive immigration reform.

Durbin said Johnson's biggest challenges are that he's "in the minority" and "overwhelmed."

"I've seen those hearings. I know that committee. It's one of the most partisan committees on Capitol Hill. They're not looking for answers. They're looking for settings so they can give their speeches," Durbin said.