Senate Democrats on Wednesday dismissed the articles of impeachment brought by House Republicans against Alejandro Mayorkas, the homeland security secretary, on grounds that the charges failed to meet the bar of “high crimes and misdemeanors” outlined in the constitution as a basis for removing an official from office.

In a pair of party-line votes, Democrats held that the articles alleging Mayorkas willfully refused to enforce border laws and breached the public trust with his statements to Congress about the high levels of migration at the US southern border with Mexico were unconstitutional. On the first article, the Alaska senator Lisa Murkowski, a Republican, voted “present”.

Democrats then voted 51-49 to adjourn the trial just one day after House Republicans presented the articles to the Senate.

“It is beneath the dignity of the Senate to entertain this nakedly partisan exercise,” Schumer said in a floor speech opening Wednesday’s session.

Constitutional scholars, including conservative legal experts, have said the Republicans’ impeachment case is deeply flawed and weakens Congress’s most powerful tool for holding despots and delinquents to account. But Republicans pushed ahead, arguing that Mayorkas’ handling of the southern border warranted a historic rebuke.

“This process must not be abused. It must not be short-circuited,” Mitch McConnell, the Senate minority leader, said, imploring Democrats to hold a full trial. “History will not judge this moment well.”

After the Senate convened as a court of impeachment, Schumer offered his plan to hold votes to dismiss the two articles of impeachment after limited debate. Senator Eric Schmitt, a Republican of Missouri, immediately objected to Schumer’s proposal and accused the Democratic leader of “setting our constitution ablaze” by seeking to dispense with the charges against Mayorkas.

The majority leader then called for votes to dismiss the trial, setting off a series of procedural maneuvers by Republicans to delay the proceedings, all of which were rejected 51-49 by the Democratic majority.

Had they moved to a trial, Republicans still would have lacked the support of two-thirds of the Senate that is needed to convict and remove Mayorkas from office.

Joe Biden has said he continues to have confidence in Mayorkas, who has denied wrongdoing.

“As they work on impeachment, I work in advancing the missions of the Department of Homeland Security. That’s what I’ve done throughout this process,” Mayorkas said on Wednesday during an appearance on CBS to discuss a new federal initiative to combat online abuse of children.

Democrats cast the impeachment effort as election-year political theater designed to draw attention to the situation at the border, one of the president’s biggest liabilities. Donald Trump, the presumptive Republican presidential nominee, has made immigration the centerpiece of his campaign for the White House.

“The impeachment of Alejandro Mayorkas has nothing to do with high crimes and misdemeanors and everything to do with helping Donald Trump on the campaign trail,” Schumer added on Wednesday.

He charged Republicans instead to join Democrats in passing the bipartisan Senate border bill aimed they derailed at Trump’s behest.

Some Senate Republicans have expressed deep skepticism of the impeachment effort. But conservatives have cried foul and are preparing to deploy a series of procedural tactics in an effort to delay the vote ending the trial without arguments.

“What Senator Schumer is going to do is fatuous, it is fraudulent and it is an insult to the Senate and a disservice to every American citizen,” said John Kennedy, Republican Senator of Louisiana, at a press conference on Tuesday.

By a single vote, House Republicans impeached Mayorkas in February for his handling of the border. It was the first time in nearly 150 years that a cabinet secretary was impeached.

But Mike Johnson delayed the transfer of the articles for several weeks, initially to allow the chambers more time to complete work on government funding legislation. Upon returning from a two-week recess, the House speaker again postponed the transfer at the request of Senate Republicans, who requested more time to prepare.

The proceedings began at 1pm, when Senator Chuck Grassley, Republican of Iowa, administered the oath of office to the Senate president pro tempore Patty Murray, a Democrat of Washington. Each senator was sworn in as a juror and signed their name in an oath book.

“Hear ye! Hear ye! Hear ye!” the sergeant-at-arms proclaimed, reminding senators that they are to “keep silent on pain of imprisonment” for the duration of the trial.

Had the Senate moved to an impeachment trial, it would be the third time in five years. Trump was impeached twice during his presidency, first over his dealings with Ukraine and later over his involvement in the January 6 assault on the US Capitol. He was acquitted both times by Senate Republicans.