WASHINGTON (Reuters) - Democrats and one Republican on U.S. congressional intelligence panels said on Wednesday after viewing a whistleblower complaint concerning President Donald Trump that the allegations were credible and troubling.

The complaint, lodged by a member of the U.S. intelligence community, centered on Trump urging Ukraine to investigate Democratic presidential front-runner Joe Biden, according to news reports.

“I found the allegations deeply disturbing. I also found them very credible,” said Democrat Adam Schiff, chairman of the House Intelligence Committee.

At least one Republican member of the Senate Intelligence Committee expressed dismay about the complaint’s contents. Senator Ben Sasse, who has been critical of fellow Republican Trump, said there were “real troubling things here.”

“Republicans ought not just circle the wagons” to protect Trump, he said after leaving a secure room where senators read the complaint.

The Democratic-led House of Representatives on Tuesday launched a formal impeachment inquiry of Trump over the Ukraine matter.

After initially resisting demands by Democrats in Congress to see the whistleblower complaint, the Trump administration relented and allowed members of the House of Representatives and Senate Intelligence committees to view it on Wednesday.

The acting director of national intelligence, Joseph Maguire, was due to testify about the issue before the House Intelligence Committee on Thursday.

Trump pressed Ukrainian President Volodymyr Zelenskiy in a July phone call to launch a probe of Biden and his son, who worked for a Ukrainian gas company. The call occurred after Trump had ordered a freeze of nearly $400 million in U.S. aid to Ukraine. A summary of the call was released by the Trump administration on Wednesday.

There has been no evidence that Biden, who served as U.S. vice president from 2009 to 2017, used his position to help his son in the Ukraine matter.

A Republican member of the House Intelligence Committee, Mike Conaway, said after reading the complaint he did not think it would compromise Trump if it was declassified.

“I haven’t seen anything that bothers me,” Conaway said.

The lawmakers declined to provide details about the classified complaint.

Lawmakers have said they hoped to hear from the whistleblower at some point, but no meeting has been scheduled.

Schiff thanked the whistleblower for coming forward. “I think that what this courageous individual has done has exposed serious wrongdoing,” he said. “We will do everything possible to protect you.”