The Senate on Wednesday dismissed the first of two articles of impeachment against Alejandro N. Mayorkas, the homeland security secretary, voting along party lines before his trial got underway to sweep aside the charge accusing him of failing to enforce immigration laws.
By a vote of 51 to 48, with one senator voting “present,” the Senate ruled that the charge was unconstitutional because it failed to meet the constitutional bar of a high crime or misdemeanor. Republicans united in opposition except for Senator Lisa Murkowski of Alaska, the lone “present” vote, while Democrats were unanimous in favor, after arguing that a cabinet member cannot be impeached and removed merely for carrying out the policies of the administration he serves.
“To validate this gross abuse by the House would be a grave mistake and could set a dangerous precedent for the future,” said Senator Chuck Schumer of New York, the majority leader.
Republicans, for their part, warned that the dangerous precedent was the one that Democrats set by moving to skip an impeachment trial altogether, which they argued was a shirking of the Senate’s constitutional duty. They tried several times to delay the dismissal, failing on a series of party-line votes.
“Tabling articles of impeachment would be unprecedented in the history of the Senate — it’s as simple as that,” said Senator Mitch McConnell of Kentucky, the minority leader.
Democrats moved immediately to strike down the second article of impeachment against Mr. Mayorkas, alleging a breach of the public trust, thus skipping the trial altogether. A vote was expected later on Wednesday.
Mr. Mayorkas is the first sitting cabinet member in United States history to be impeached. William Belknap, the secretary of war, was impeached in 1876, but he resigned just minutes before the scheduled vote.
Unlike Mr. Belknap, Mr. Mayorkas was never accused of corruption or of any crime other than carrying out immigration policies that Republicans oppose.
Democrats have denounced the impeachment of Mr. Mayorkas as illegitimate and politicized. Legal experts have called the case against him groundless, arguing that the accusations against him do not rise to the level of impeachable offenses. But Republicans pushed forward anyway in what was essentially a bid to blame the secretary for President Biden’s immigration policies, which they contend have fueled a wave of illegal migration.
The vote came after Republicans spent much of the day railing against chaos at the southern border and blaming the Biden administration for it. Under Mr. Biden, crossings at the southern border have reached record highs. Republicans insisted Mr. Schumer hold a trial in which House impeachment managers would lay out their accusations.
Failing to do so, Mr. McConnell said, “would mean running both from our fundamental responsibility and from the glaring truth of the record-breaking crisis at our southern border.”
Mr. McConnell did not mention that he voted in favor of an unsuccessful Republican effort in 2021 to dismiss a second impeachment case against Mr. Trump over the Jan. 6 attack on the Capitol before the Senate held a trial.
On Wednesday, the Senate prepared to transform itself into a court of impeachment, with senators sworn in on the floor and required to sit at their desks to begin the proceeding. But they spent much of the afternoon haggling over whether to have the trial at all.
Republicans expressed outrage at the failure to do so. After the first charge was dismissed, Senator Mike Lee, Republican of Utah, rose on the floor and angrily demanded, “If this is not a high crime and misdemeanor, what is?”
Mr. Mayorkas has spent months essentially ignoring the case and continuing to work. He negotiated a border security deal with both Senate Republicans and Democrats that fell apart after former President Donald J. Trump opposed it.
Mr. Mayorkas spent Tuesday on Capitol Hill talking about his agency’s budget request and calling on Congress to provide the department with more resources to enforce border laws, hire more personnel and pass the legislation he negotiated.