WASHINGTON (Reuters) - President Donald Trump on Wednesday stepped up his defense of his U.S. Supreme Court nominee, saying it was hard to imagine Brett Kavanaugh committed a sexual assault and that it would be unfortunate if his accuser did not testify before the Senate.

With Trump’s effort to cement conservative control of the nation’s highest court on a knife’s edge, Senate Judiciary Committee Chairman Chuck Grassley set a Friday morning deadline for Christine Blasey Ford to decide if she will talk to lawmakers.

Ford, a psychology professor at Palo Alto University in California, has said Kavanaugh, a federal appeals court judge, sexually assaulted her in 1982 when both were high school students in Maryland. Kavanaugh has called Ford’s allegation “completely false.”

If Ford opts not to testify, Kavanaugh’s chances for confirmation in the Republican-led Senate could be boosted, with senators in Trump’s party so far remaining largely supportive.

“I think it’s not fair to Judge Kavanaugh for her not to come forward and testify,” moderate Republican Senator Susan Collins, whose vote could be crucial, said in a radio interview.

Grassley’s committee wants prepared testimony from Ford by Friday and an answer on whether she will accept its invitation to testify to the panel on Monday, either publicly or privately. The committee also has invited Kavanaugh to testify on Monday.

Ford’s lawyers said on Tuesday she would testify before the committee only if the FBI first investigated her allegation. The FBI has said it is not investigating the matter, a decision backed by Republicans.

“It is not the FBI’s role to investigate a matter such as this,” wrote Grassley, who also sent a letter to committee Democrats formally rejecting their bid for the FBI to investigate.

Later on Wednesday, Grassley wrote to the senior Democrat on the committee, Dianne Feinstein, requesting she immediately provide an unredacted copy of the letter Ford sent her in July about the assault allegation, saying he must review it before Monday’s hearing.

‘MULTIPLE WITNESSES’

In a statement on Wednesday, a lawyer for Ford said her client was willing to cooperate with the committee, but criticized its plan to have only Ford and Kavanaugh testify.

“There are multiple witnesses whose names have appeared publicly and should be included in any proceeding,” Ford’s lawyer Lisa Banks said.

“The rush to a hearing is unnecessary, and contrary to the committee discovering the truth,” Banks said.

Ford’s allegation has jeopardized Kavanaugh’s nomination to the lifetime post on the Supreme Court, which previously was on track toward confirmation.

“Look, if she shows up and makes a credible showing, that will be very interesting and we’ll have to make a decision,” Trump told reporters at the White House.

“But I can only say this: He’s such an outstanding man - very hard for me to imagine that anything happened,” Trump said.

“If she shows up, that would be wonderful. If she doesn’t show up, that would be unfortunate,” Trump added, calling the situation “very unfair” to his nominee.

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Ford has accused Kavanaugh of attacking her and trying to remove her clothing while he was drunk at a party in 1982 when he was 17 years old and she was 15. Ford’s lawyers said in a letter to Grassley on Tuesday she had faced “vicious harassment and even death threats” since coming forward on Sunday. Grassley said he was disturbed to learn of the threats.

The confirmation fight comes just weeks before Nov. 6 congressional elections in which Democrats are seeking to win control of Congress from the Republicans.

Any defections from the Republicans’ narrow Senate majority could sink the nomination and deal a major setback to Trump, who has been appointing more conservatives to the high court and the broader federal judiciary.

Democratic U.S. Senator Claire McCaskill, who faces a tough re-election battle in Missouri, which Trump won in the 2016 presidential election, said on Twitter on Wednesday that she would vote against Kavanaugh’s confirmation because of “his positions on several key issues, most importantly the avalanche of dark, anonymous money that is crushing our democracy.”

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‘FINDING THE TRUTH’

Republican panel member Lindsey Graham said on Twitter that requiring an FBI investigation of a 36-year-old allegation “is not about finding the truth, but delaying the process till after the midterm elections.”

The Justice Department has said the FBI sent Ford’s initial letter making the allegation against Kavanaugh to the White House and considers its role in the matter complete.

Democrats have said the White House can order a more detailed FBI investigation, as occurred during the 1991 confirmation process for Supreme Court Justice Clarence Thomas after he was accused of sexual harassment. Republicans have said the FBI would be doing nothing more than what committee staffers could achieve by interviewing Kavanaugh and Ford.

A Reuters/Ipsos poll released on Wednesday showed a growing number of Americans opposing Kavanaugh’s nomination. In the poll, conducted from Sept. 11-17, 36 percent of U.S. adults surveyed did not want Kavanaugh on the Supreme Court, up 6 percentage points from a similar poll a month earlier, while 31 percent favored Kavanaugh’s appointment.

Palo Alto University issued a statement supporting Ford. The university’s president called Ford’s decision to come forward courageous.

Committee Republicans have planned for only Kavanaugh and Ford to testify, but Democrats want other witnesses, too.

Democratic Senator Doug Jones said Mark Judge, Kavanaugh’s high school friend, should be subpoenaed if he refuses to testify. Ford has said Judge witnessed the alleged assault.

Judge’s lawyer said in a letter to the committee on Tuesday that Judge did not recall the incident and did not wish to testify.