Grassley is having none of it. He said Tuesday that the fact that the individual’s knowledge of Trump’s phone call and the White House restricting records came secondhand should not invalidate his reporting.

“This person appears to have followed the whistleblower protection laws and ought to be heard out and protected. We should always work to respect whistleblowers,” Grassley said. “Complaints based on second-hand information should not be rejected out of hand, but they do require additional leg work to get at the facts and evaluate the claim’s credibility.”

Grassley also said media reports on the identity of the whistleblower “don’t serve the public interest—even if the conflict sells more papers or attracts clicks.” The New York Times and Washington Post both reported that the whistleblower is a CIA officer but did not identify him by name.

For now, Grassley is something of a lonely voice in the party, though Maine Sen. Susan Collins pushed back forcefully against Trump’s suggestion last week that the whistleblower’s sources are spies. The whistleblower claimed administration sources said Trump moved to “abuse his office for personal gain” when speaking to Ukrainian President Volodymyr Zelensky about former Vice President Joe Biden in July, then tried to restrict access to the call-record of the conversation. The complaint and a transcript of the call are the basis for House Democrats' impeachment inquiry.

On Tuesday at a short Senate session, Sen. Josh Hawley (R-Mo.) said he left it up to reporters as to whether the media should reveal more about the whistleblower and said much more should be learned about this person.

“I’d assume if you were going to dig into this you’d want to know who the sources are that the whistleblower relied on. And I’d assume we’d want to know whom the whistleblower himself or herself is and if they’re credible,” Hawley said.

Last week, a number of Republicans mounted attacks on the whistleblower as a secondhand source with no direct knowledge of the inner workings of the administration.

“He’s not really a whistleblower, so it’s really more hearsay,” South Carolina Sen. Tim Scott said Friday.

Grassley said “the distinctions being drawn between first and secondhand knowledge aren’t legal ones.” He did not mention Trump or his attacks on the whistleblower specifically in his statement, instead asserting that “no one should be making judgments or pronouncements without hearing from the whistleblower first and carefully following up on the facts.”

The intelligence community's inspector general pushed back Monday against reports and comments from conservative media and politicians that said the whistleblower complaint system was recently changed.

Grassley has made sure to bring up whistleblowers in public forums with the Trump administration. He said earlier this year he asked Attorney General William Barr in a meeting how he would handle whistleblower complaints as attorney general. Barr was confirmed by the Senate this year with Grassley’s support.

“They all say they’re going to respect whistleblowers but they end up not doing it,” Grassley said of administration officials. “ Every Cabinet person that comes in is well intended about protecting whistleblowers and then they’re treated like a skunk at a picnic.”

Trump has suggested he wants to find out the identity of the whistleblower, who issued a complaint on Aug. 12 to congressional intelligence committees about Trump leaning on Ukraine’s president to investigate Biden, a leading political rival.

“So if the so-called ‘Whistleblower’ has all second hand information, and almost everything he has said about my ‘perfect’ call with the Ukrainian President is wrong (much to the embarrassment of Pelosi & Schiff), why aren’t we entitled to interview & learn everything about the Whistleblower, and also the person who gave all of the false information to him,” Trump tweeted on Tuesday. “This is simply about a phone conversation that could not have been nicer, warmer, or better."

Thus far, Republicans who are defending the president are largely relying on the White House summary of his call with Zelensky in July, which they say shows no explicit quid pro quo and is just how Trump talks.

“I don’t see any evidence yet of any crime. Or any evidence approaching a crime. If there is any evidence or if there are any actual facts to that effect, I hope somebody will come forward with them. But what we have right now is a bunch of speculation,” Hawley said. “We do have the transcript. It’s the only actual hard piece of data that we’ve got. It doesn’t show a crime.”

And despite being on opposite pages with Trump, Grassley made clear in his statement he is not endorsing Speaker Nancy Pelosi’s impeachment inquiry approach, either. On Monday, he also sided firmly with conservatives when his office made public a letter from Grassley and Sen. Ron Johnson (R-Wis.) in which the senators asked Barr to investigate any ties between Ukraine and Hillary Clinton's 2016 campaign.

On Tuesday, in his statement on the whistleblower, Grassley's message was essentially that everyone should slow down.

“Uninformed speculation wielded by politicians or media commentators as a partisan weapon is counterproductive and doesn’t serve the country,” Grassley said. “Inquiries that put impeachment first and facts last don’t weigh very credibly. Folks just ought to be responsible with their words.”

Marianne LeVine contributed to this report.