WASHINGTON (AP) — 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 argued Tuesday that forgoing a full Senate trial would break precedent, most Senate Republicans voted to do 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. Their effort to halt the proceedings failed. Trump was ultimately acquitted in the Senate trial.

"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.

"Ultimately, I think it's virtually certain that there will not be the conviction of someone when the constitutional test has not been met," said Sen. Mitt Romney, R-Utah.

Romney said he was not sure how he would vote on the Senate's process but wanted to at least express his view that "Mayorkas has done a terrible job, but he's following the direction of the president and has not met the constitutional test of a high crime or misdemeanor."

Still, with elections approaching, Republicans want to force Congress to grapple with the Biden administration's handling of the southern border as long as possible.

"I think there are a lot of Democrats who really want to avoid the vote. I don't blame them. I mean, this is the number one issue on the minds of Americans," Thune said.

Sen. Sherrod Brown, a Democrat who is facing a tough reelection bid in Ohio, called the impeachment trial a "distraction" and pointed to Republican senators rejecting a bipartisan deal aimed at tamping down the number of illegal border crossings from Mexico.

"Instead of doing this impeachment — the first one in 100 years — why are we not doing a bipartisan border deal?" Brown said.

Prior to Mayorkas, only one U.S. cabinet official had ever been impeached. Secretary of War William Belknap in 1876. A House investigation found evidence that he had received kickback payments while administering government contracts.

Belknap resigned, but the Senate still held a trial. The votes on all five impeachment charges against Belknap fell short of the two-thirds majority needed for a conviction.