WASHINGTON — Speaker Mike Johnson will delay sending the House’s articles of impeachment against Homeland Security Secretary Alejandro Mayorkas to the Senate this week as previously planned after Republican senators requested more time Tuesday to build support for holding a full trial.

The sudden change of plans cast fresh doubts on the proceedings, the historic first impeachment of a Cabinet secretary in roughly 150 years. Seeking to rebuke the Biden administration’s handling of the southern border, House Republicans impeached Mayorkas in February, but delayed sending the articles while they finished work on government funding legislation.

Johnson had planned to send the impeachment charges to the Senate on Wednesday evening. But as it became clear that Democrats, who hold majority control of the chamber, had the votes to quickly dismiss them, Senate Republicans requested that Johnson delay until next week. They hoped the tactic would prolong the process.

While Republicans have argued against a speedy dismissal of charges, most Senate Republicans did just that when Donald Trump, the former president, was impeached a second time on charges he incited an insurrection in the Jan. 6, 2021, attack on the Capitol. He was ultimately acquitted.

“Our members want to have an opportunity not only to debate but also to have some votes on issues they want to raise,” said South Dakota Sen. John Thune, the second-ranking Republican Senate leader. Under procedural rules, senators are required to convene as jurors the day after the articles of impeachment are transmitted for a trial.

“There is no reason whatsoever for the Senate to abdicate its responsibility to hold an impeachment trial,” Johnson’s spokesman, Taylor Haulsee, said in a statement announcing the delay.

Senate Majority Leader Chuck Schumer. D-N.Y., who has decried the impeachment push as a “sham,” suggested Democrats still plan to deal with the charges quickly.

“We’re ready to go whenever they are. We are sticking with our plan. We’re going to move this as expeditiously as possible,” Schumer said.

“Impeachment should never be used to settle policy disagreements,” he told reporters earlier Tuesday.

House Republicans charged in two articles of impeachment that Mayorkas has not only refused to enforce existing law but also breached the public trust by lying to Congress and saying the border was secure.

Democrats — and a few Republicans — say the charges amount to a policy dispute, not the Constitution’s bar of high crimes and misdemeanors.