WASHINGTON — The FBI has again been thrust to the center of the day’s biggest political controversy after President Donald Trump and Republican Senate leaders agreed to allow the bureau to conduct an additional background check of Brett Kavanaugh, whose nomination to the Supreme Court hangs in the balance over allegations of sexual misconduct.

The probe is considered a part of Kavanaugh’s background check because the allegations are from Kavanaugh’s teenage years and the activity does not involve any federal crimes, officials said.

That is important because, unlike in a criminal investigation, additional work had to be requested by the White House, which is allowed to impose parameters on the scope, officials said.

The FBI also is following up on allegations by Christine Blasey Ford, a psychology professor at Palo Alto University in California, who testified to the Senate last week that Kavanaugh sexually assaulted her in the early 1980s when they were in high school in suburban Washington, D.C.

Ford recounted in detail how Kavanaugh and his friend Mark Judge allegedly attacked her in a bedroom during a small gathering at a house when the teen boys were both drunk.

After Ford’s testimony, Kavanaugh vigorously denied the allegations before the committee and accused Democrats of launching a last-minute attempt to derail his nomination. He decried the confirmation process as a “circus.”

According to people familiar with the unfolding investigation, the FBI has also begun contacting other people, including a second woman who alleges that the Supreme Court nominee sexually assaulted her.

The bureau has reached out to Deborah Ramirez, a Yale University classmate of Kavanaugh’s who alleges that he shoved his genitals in her face at a party where she had been drinking and became disoriented, her attorney said Saturday.

“She has agreed to cooperate with their investigation,” Ramirez attorney John Clune said in a statement. “Out of respect for the integrity of the process, we will have no further comment at this time.”

From the probe of Hillary Clinton’s use of a private email server to the examination of Trump’s presidential campaign, the FBI has grown accustomed in recent months to conducting investigations that are viewed through sharply partisan lenses. The case of Kavanaugh, though, presents significant challenges.

The allegations against the Supreme Court nominee are decades old, and his accusers say their memories — sometimes of dates and locations — are hazy. A background check is not like a criminal investigation; investigators would not use tools such as grand juries, subpoenas and search warrants, meaning potential witnesses could simply decline to be interviewed.

The FBI will ultimately report its findings — which, in Kavanaugh’s case, will probably be mostly reports of interviews — to the White House. The bureau will not conclude whether the accusers are believable or not, or tell the White House whether it should withdraw Kavanaugh’s nomination.

The FBI’s findings will not necessarily become public. When investigators have completed their work, anything they’ve discovered will be turned over to the White House as an update to Kavanaugh’s background check file. The White House would then likely share the material with the Senate committee.

At that point, all senators, as well as a very small group of aides, would have access to it.

The FBI’s interviews, which will take a few days to conduct, won’t turn into a sprawling inquest of everyone Kavanaugh went to a party with in high school, said a person familiar with the investigation.

But already, two potentially crucial witnesses have said they will cooperate with the FBI, raising the possibility that at least more statements and recollections will be added to the record, even if they’re not ultimately definitive.

Judge, the high school friend of Kavanaugh who Ford says was in the room during the alleged assault, has also agreed to cooperate with the FBI. His account has been sought after because, unlike Kavanaugh, Judge has not denied Ford’s allegations but has said he has no memory that such an assault occurred.

“They’re not going to crack the case,” said Ron Hosko, a former assistant FBI director. “The best they can hope to do is find the facts, relay the statements of the witnesses that presumably would be later tested if Congress chose to do so and the president greenlighted it.”

That is not to say an FBI investigation will not yield new information. Witnesses who have provided only brief statements to Congress might be more willing to cooperate with law enforcement.

Judge and others will have a strong incentive to tell the truth. Lying to the FBI is a federal crime. FBI agents are also trained specifically to investigate such matters. Their detailed inquiries will probably reveal answers to questions in a way that partisan congressional hearings cannot.

Once the White House gives Congress the FBI’s report, lawmakers might decide to hold a hearing or change their vote. If investigators uncover evidence that Kavanaugh lied to lawmakers during hearings or on his background-check forms, that could spark a criminal investigation in which law enforcement could use the full extent of its legal powers.

In addition to Ford and Ramirez, another woman, Julie Swetnik, who said she knew Kavanaugh in high school, alleged in a sworn statement last week that Kavanaugh and Judge got teenage girls drunk at parties, where the girls were sexually assaulted, sometimes by groups of boys.

Swetnik claimed that she was raped by such a group at a party where Kavanaugh and Judge were present. She hasn’t accused Kavanaugh of raping her. Swetnik described Kavanaugh as a “mean drunk” in high school who was physically and verbally aggressive with girls.

Swetnik’s attorney, Michael Avenatti, said she had not yet been contacted by the FBI but that he hopes to hear from investigators.

“I don’t know how this investigation could be called complete if they don’t contact her,” Avenatti said.

Kavanugh has denied the accusations from Ramirez and Swetnik and has said that he never abused or assaulted anyone.