Senator Cory Booker, visibly tired but still upright at a lectern on the Senate floor, was deep into the second day of a speech criticizing the Trump administration on Tuesday, a show of physical and oratorical stamina that he hoped would spotlight what he called a “crisis” facing the United States under President Trump.

Mr. Booker, Democrat of New Jersey, began speaking at 7 p.m. on Monday and was still going more than 24 hours later, laying into the Trump administration’s cuts to government services and its crackdown on immigrants.

“This is not right or left, it is right or wrong,” Mr. Booker said on Tuesday afternoon, his voice still strong. “This is not a partisan moment, it is a moral moment. Where do you stand?”

The speech was part of an effort by Democrats to retake the initiative and more assertively oppose President Trump. Mr. Booker divided his remarks into sections focused on an aspect of the administration’s policies, including on health care, education, immigration and national security.

By Tuesday afternoon, Mr. Booker appeared to be pressing to break a record set by Senator Strom Thurmond, who in 1957 delivered a 24-hour-18-minute filibuster opposing a piece of civil rights legislation. Mr. Booker, who for weeks had contemplated giving a marathon floor speech, has long been bothered that Mr. Thurmond, a segregationist from South Carolina, held the record, according to Mr. Booker’s office. (The Senate’s log of longest speeches does not reach back to the founding of the nation, but Mr. Thurmond’s is the longest on record.)

By 4:20 p.m., Mr. Booker’s speech had passed Senator Ted Cruz’s memorable harangue of President Barack Obama’s Affordable Care Act in 2013, which lasted 21 hours and 19 minutes.

Mr. Booker’s speech was not a filibuster — a procedural tactic that has been used to block legislation on many issues — because it did not come during a debate over a specific bill or nominee. But it did delay a planned vote on a Democratic-led bill to undo Mr. Trump’s tariffs on Canada.

“I rise with the intention of disrupting the normal business of the United States Senate for as long as I am physically able,” Mr. Booker said near the start of his speech on Monday. “I rise tonight because I believe sincerely that our nation is in crisis.”

He assailed what he said were Mr. Trump’s plans to cut funding for Medicaid, among other programs. The White House has denied that it plans to cut Medicaid benefits, but the president and his allies have attacked Medicaid, Medicare and Social Security over what they claim is waste, fraud and abuse.

Going without bathroom breaks but taking occasional pauses for encouraging questions from his fellow Democrats, Mr. Booker read from a binder of notes and waved a small copy of the U.S. Constitution. Over the hours, Mr. Booker’s voice grew hoarse. But it continued to boom.

“My voice is inadequate,” Mr. Booker said. “My efforts today are inadequate to stop what they’re trying to do. But we the people are powerful.”

Before his speech, Mr. Booker said on social media that he was heading to the Senate floor because Mr. Trump and Elon Musk, the billionaire who is one of the president’s top advisers, had shown what he called “a complete disregard for the rule of law, the Constitution and the needs of the American people.”

Mr. Musk’s feed on X was active Tuesday, but it made no mention of Mr. Booker or his all-night speech. Neither did Mr. Trump’s Truth Social feed.

But a White House spokesman, Harrison Fields, said that Mr. Booker was seeking an “I am Spartacus” moment, referring to a comment by Mr. Booker during the Supreme Court confirmation hearings for Brett Kavanaugh that was mocked by conservatives as a bid by Mr. Booker to capture a viral moment.

“When will he realize he’s not Spartacus — he’s a spoof?” Mr. Fields said in a statement.

As thousands of viewers followed on Mr. Booker’s official YouTube channel, he quoted from celebrated speeches by Representative John Lewis and Senator John McCain, both of whom have died. At one point, he spent around 30 minutes reading an account by a Canadian citizen, Jasmine Mooney, about her detention in the United States by immigration enforcement officers.

Since 1915, many of the 48 all-night sessions in the chamber — defined as those lasting past 4 a.m. — have gone well over 24 hours.

Mr. Booker would surpass Mr. Thurmond’s Senate record at 7:19 p.m.

Mr. Thurmond was sustained by orange juice and bits of beef and pumpernickel during his speech. It was not clear if Mr. Booker had eaten anything on Tuesday, but two glasses of water rested on a desk in front of his lectern.

Maya C. Miller and Robert Jimison contributed reporting.