WASHINGTON — Top House Democrats, anxiously awaiting the findings of the special counsel, Robert S. Mueller III, insisted on Sunday that their own investigations must go on regardless of whether the Justice Department accuses President Trump of wrongdoing.

Expecting the “principal conclusions” of Mr. Mueller’s 22-month investigation to be made public by Attorney General William P. Barr as soon as Sunday afternoon but lacking any information on its findings, they sought to play down Mr. Mueller’s investigation into Russia’s election interference and possible ties to the Trump campaign as a relatively narrow endeavor that does not relieve Congress of its own oversight responsibility.

“The job of Congress is much broader than the job of special counsel,” Representative Jerrold Nadler of New York, the House Judiciary Committee chairman, said on “Fox News Sunday.” “The special counsel was looking and can only look for crimes. We have to protect the rule of law. We have to look for abuses of power. We have to look for obstruction of justice. We have to look for corruption.”

Mr. Nadler said that Congress must see Mr. Mueller’s full report and evidence — not just a summary from Mr. Barr — and that he would use a subpoena and take the fight to the Supreme Court if necessary to secure those.