WASHINGTON — A pair of undeclared Republican senators accepted a confidential new FBI report into sex-abuse allegations against Brett Kavanaugh on Thursday as “thorough,” bolstering GOP hopes for confirmation as the Senate plunged toward showdown votes on President Donald Trump’s embattled Supreme Court nominee.

One of the senators hinted he was open to supporting Kavanaugh as party leaders pushed for winning results in a preliminary vote today and a final Senate roll call by this weekend.

Six days after Trump reluctantly ordered the FBI to scrutinize the allegations — which Kavanaugh has denied — leading GOP lawmakers briefed on the agency’s confidential document reached the same conclusion: There was no verification of the women’s past claims and nothing new.

Democrats complained that the investigation was shoddy, omitting interviews with numerous potential witnesses, and accused the White House of limiting the FBI’s leeway. Those not interviewed in the reopened background investigation included Kavanaugh himself and Christine Blasey Ford, who ignited the furor by alleging he’d molested her in a locked room at a 1982 gathering of high school students.

A week after a televised Senate Judiciary Committee hearing at which Kavanaugh and Ford transfixed the nation, the Capitol campus remained a stew of tension. A hefty police presence added an air of anxiety, as did thousands of noisy anti-Kavanaugh demonstrators who gathered outside the Supreme Court and in a Senate office building.

Capitol Police said that more than 300 people had been arrested Thursday for “unlawfully demonstrating in the atrium of the Hart Senate Office Building” and charged with “crowding, obstructing or incommoding.” Among those detained may have been Towson alum and comedian Amy Schumer. In a video posted to Twitter on Thursday afternoon, Schumer said: “I think we’re going to get arrested.” Police could not confirm that Schumer had been arrested because of the large number of people taken into custody. Schumer identifies as a sexual assault survivor and has been vocal on social media about her opposition to Kavanaugh in recent weeks.

In Harford County, several dozen protestors stood at the intersection of South Main Street and Churchville Road in Bel Air on Wednesday, holding signs as evening rush hour traffic passed. They chanted slogans like “We believe survivors” and “Kavanaugh lied, then he fake cried, he is not bona fide,” referring to his emotional testimony before the Senate Judiciary Committee.

Khiyali Pillalamarri, a 15-year-old student at Aberdeen High School attended the protest, which was organized by Together We Will Harford County/Upper Chesapeake. “Being 15, it is kind of frightening that this [assault] happened [to Ford] when she was 15,” Khiyali said.

Senate Majority Leader Mitch McConnell, R-Ky., set course for his chamber to hold a crucial test vote today and, should that succeed, final confirmation Saturday. “What we know for sure is the FBI report did not corroborate any of the allegations against Judge Kavanaugh,” McConnell told reporters about the document, which was sent to Congress overnight. On the Senate floor, he witheringly called the accusations “uncorroborated mud.”

Earlier, Sen. Jeff Flake of Arizona, one of the publicly undecided Republicans, told reporters that “we’ve seen no additional corroborating information” about the claims against the 53-year-old conservative jurist and said the investigation had been comprehensive.

A second undeclared Republican, Susan Collins of Maine, also expressed satisfaction with the probe, calling it “a very thorough investigation” and paid two visits to the off-limits room where the document was being displayed to lawmakers. Sen. Lisa Murkowski, R-Alaska, said she was “still reviewing” her decision.

While GOP leaders were not saying they’d nailed down the support needed, two “yes” votes from among Flake, Collins and Murkowski would ensure Kavanaugh’s confirmation because every other Republican was poised to back him. Republicans have a narrow 51-49 Senate majority, and Vice President Mike Pence will be available to cast a tie-breaking vote.

The trio of GOP moderates, leery of three women’s claims of alcohol-fueled sexual misconduct by Kavanaugh, had refused to let his nomination proceed last week until Trump ordered the FBI probe. The three were briefed together on the investigation in the secure room senators were using to view the report.

Underscoring the hardening partisan lines, one of the two undecided Democratic senators said she’d oppose Kavanaugh. North Dakota Sen. Heidi Heitkamp, who faces a difficult re-election race next month, cited concerns about his “past conduct” and said she felt his heated attacks on Democrats during last week’s Judiciary Committee hearing raised questions about his “current temperament, honesty and impartiality.”

West Virginia’s Joe Manchin, the other undeclared Democrat, spent time looking at the report and said he would resume reading it today.

Sen. Dianne Feinstein of California, the Judiciary Committee’s top Democrat, said while her party had agreed to a weeklong FBI probe with a finite scope, “we did not agree that the White House should tie the FBI’s hands.”

Democrats also objected to a statement by committee Chairman Chuck Grassley, R-Iowa, who said the investigation “found no hint of misconduct.” The Judiciary panel’s 10 Democrats said in a statement that based on their briefing and study of the document, “That is not true.”

Initially, the FBI was asked to interview four witnesses. Three — Mark Judge, Peter Smyth and Leland Keyser — were at the gathering where Ford said Kavanaugh pushed her onto a bed and groped at her. The fourth, Deborah Ramirez, had separately alleged that Kavanaugh exposed his penis to her when both were students at Yale.

The limited breadth, though, sparked significant controversy, and the White House soon permitted the FBI to expand its investigation — albeit only modestly. The White House, for example, barred a broad look at Kavanaugh’s youthful drinking and whether he had misled the Senate in testifying about it, the people familiar with the process said. Some Republican senators insisted Thursday that the FBI was allowed to interview those the agency deemed appropriate.

Agents also talked to two other men, Tim Gaudette and Chris Garrett, who were listed on a calendar as being with Kavanaugh at a gathering at a house on July 1, 1982.

The bureau also interviewed three other people, whose names have not yet been made public, according to the White House. Notably, though, agents did not talk to Ford herself, nor did they interview the more than a dozen other people whose names Ford’s legal team provided to the bureau. The legal team said those people would have challenged the credibility of Kavanaugh’s Senate testimony or provided other information to support Ford’s account.

If agents had interviewed those people, a member of Ford’s legal team told The Washington Post, they might have learned that Ford was never focused on July 1 as the date that the assault occurred.

Ramirez’s legal team, similarly, said that it provided the FBI with a list of more than 20 possible witnesses and that it was unaware of the FBI following up with those people.

Several former Yale students have said they got in touch with the FBI proactively offering various bits of information but were never formally interviewed.

White House spokesman Raj Shah rebuffed Democrats’ complaints, saying, “What critics want is a never-ending fishing expedition into high school drinking.” He said the FBI reached out to 10 people and interviewed nine, including “several individuals at the request of the Senate, and had a series of follow-up interviews following certain leads.”

In a rare instance of a retired Supreme Court justice weighing in on a pending nomination, The Palm Beach Post quoted John Paul Stevens as saying Kavanaugh shouldn’t be confirmed because of his potential political bias. Stevens, 98, has praised Kavanaugh before, but in remarks to a group of retirees in Florida, said: “I feel his performance in the hearings ultimately changed my mind.”

Trump, who Wednesday scornfully mocked Ford’s Judiciary panel testimony, tweeted that Kavanaugh’s “great life cannot be ruined by mean” and “despicable Democrats and totally uncorroborated allegations!”

Baltimore Sun Media Group reporter David Anderson contributed to this article.