WASHINGTON — Some of President Trump’s most relentless defenders are expressing a sense of déjà vu over the impeachment inquiry currently underway.
“ORCHESTRATED DEM CAMPAIGN LIKE KAVANAUGH,” Rudolph W. Giuliani, the president’s personal lawyer, wrote on Twitter. “I’ve seen this movie before — with Brett #Kavanaugh,” said Senator Lindsey Graham of South Carolina.
“Kavanaugh 2.0” is how the National Republican Congressional Committee and the Fox News host Tucker Carlson have branded the investigation into Mr. Trump, initiated last month by Speaker Nancy Pelosi after it surfaced that Mr. Trump had made a private call to the president of Ukraine and asked him to look into a political rival, former Vice President Joseph R. Biden Jr.
The comparison to Justice Brett M. Kavanaugh’s heated confirmation last fall, which was nearly derailed by allegations of sexual assault, may prove useful for Republicans who want to cast the impeachment inquiry as yet another partisan character assassination — and one that will similarly fail. But the two events are, by nature, very different battles.
For one, the White House’s response to impeachment has concerned many Republicans, who view it as lacking focus, urgency and coordination. This suggests that the president and his allies could find it challenging to rally the same kind of unified support that helped them overcome the Democratic opposition to Justice Kavanaugh.
Last year, the operation to defend the Supreme Court nominee against allegations of sexual assault was swiftly executed and well funded, bringing together the most disparate parts of the conservative movement.
It was also notably not a pro-Trump effort. Conservatives, many of whom have long harbored misgivings about the president’s conduct, united in defense of Justice Kavanaugh, whom they saw as one of their own — a trusted, churchgoing family man who had been smeared, with decades-old stories from his high school days, as part of a liberal plot to prevent the Supreme Court from tilting any further to the right.
Impeachment, on the other hand, is different in that it will likely serve as a referendum on Mr. Trump’s presidency, especially as it centers on allegations from earlier this year — not three decades ago. Ultimately, that means Republican members of Congress would have to decide whether they are comfortable saying, in effect, that it is perfectly fine for a president to use the power of the office to solicit foreign intervention in an election.
“They can’t avoid it — they have to say this is either acceptable or it’s not,” said William Kristol, the conservative writer who was one of many “Never Trump” Republicans who found themselves in rare agreement with the Trump administration over the Kavanaugh confirmation.
Almost every Republican in Congress currently believes that Mr. Trump deserves no punishment for his dealings with Ukraine — a position consistent with the accommodating attitude the party has generally had toward his behavior. But the growing number of Americans who say they now support the impeachment inquiry — including a small but rising number of Republicans in some polls — is reason to believe that some pro-Trump lawmakers may be feeling some pressure to rethink their position.
“I don’t think this is like Kavanaugh, and that’s why the polling has moved,” Mr. Kristol said. “This is about Trump,” he added.
The Kavanaugh comparison stems in part from a belief among many Republicans that the Democrats’ attempt to block the confirmation was “a dry run for impeachment,” as some of the president’s backers said at the time.
Polls showed then that Republican voters overwhelmingly stuck with Justice Kavanaugh, and that the allegations actually led to rising support within the party for his confirmation. By the time the Senate voted, some polls found that close to 90 percent of Republicans backed him.
Some Republicans believe a similar dynamic will play out with impeachment. “I think if a Republican Senate had failed to confirm Brett Kavanaugh, it would have dramatically depressed conservative and evangelical enthusiasm,” said Ralph Reed, an evangelical leader and White House ally. “Similarly, if the conservative and evangelical grass-roots see Republicans in the House and the Senate fail to defend the president, I think it’s going to affect them adversely.”
In interviews, other allies of the president who were instrumental in the Kavanaugh fight said that the impeachment inquiry was a much different and, in some ways, more difficult case for them to defend in the court of public opinion because of its complexity.
Much of Mr. Trump’s public response, and the defense from his surrogates, has focused on the process of impeachment rather than the actual facts of the case. But it is harder to rally public support around questions of due process and fairness than it is to simply insist that the president has committed no wrongdoing.
Part of what was so simple about the Kavanaugh case was that conservatives believed him over his accuser. But when it comes to the Ukraine episode, polls have shown that the public thinks Mr. Trump has not been truthful about his actions.
And the president has vacillated repeatedly. He has called the House process a “kangaroo court.” Then he vowed to cooperate, insisting he had nothing to hide, only to have the White House announce that neither he nor the executive branch would willingly provide testimony or documents because House Democrats were not following established precedent on impeachment and were denying Mr. Trump due process.
Conservative activists said they sometimes found it difficult to follow the lead of the White House, which has sent mixed signals about how seriously it is taking the prospect that Mr. Trump could be impeached. At a closed-door conference last weekend in New Orleans for the Council for National Policy, a group of conservative movement leaders, Vice President Mike Pence made no mention of impeachment during his speech, which struck some attendees as unusual.
Republicans also had a significant procedural advantage during the Kavanaugh hearings: As the majority in the Senate, they had the sole discretion to set the timetable, which they kept extremely short — to just nine days. But they will not have such an advantage during the first portion of any impeachment proceedings, which House Democrats will dictate.
Ms. Pelosi has vowed to move the investigation along as quickly as possible and would like a vote before the end of the year. But Republicans have been left guessing, along with the rest of the country, about what the investigation might uncover or who else might come forward. This uncertainty has made settling on a messaging strategy more complicated and not as efficient as it might otherwise be.
“If there’s this idea that at the outset it’s been slow, that’ll come around,” said David Bozell, president of ForAmerica, a conservative consulting firm that specializes in social media. Mr. Bozell acknowledged that so far, Mr. Trump’s usual Republican critics like Senator Ben Sasse of Nebraska have not been as helpful as they were during the Kavanaugh confirmation. Mr. Sasse, for instance, backed Mr. Kavanaugh but has said he is troubled by the president’s efforts to solicit foreign help with his re-election.
But Mr. Bozell noted that those critics never seem to have much of an impact on the president’s standing with voters anyway.
Mostly, he and other conservative activists do not seem overly worried. When the White House counsel, Pat A. Cipollone, wrote a searing letter last week to House Democrats saying that the president would not participate in such a “partisan and unconstitutional inquiry,” administration officials convened a conference call with conservative activists to brief them on it.
Only about two dozen joined the call, one participant said, a lower figure compared to other similar calls. And when White House officials asked at the end of the call if anyone had any questions, no one spoke up.
Still, there are signs that the outlook for Mr. Trump is not improving. Support for impeaching the president has been growing among Americans who were once against it. Before the Ukraine revelations, said Whit Ayres, a Republican pollster, about 15 percent of Americans who disapproved of Trump’s job performance still opposed his impeachment and removal.
“The Ukraine revelations are reducing that number,” he said, to 12 percent in the latest NBC News/Wall Street Journal poll. “The progression of this story will likely make the impeachment inquiry numbers look much like Trump’s job approval numbers, with 40 to 45 percent opposing it and 55 to 60 percent supporting it,” Mr. Ayres added.
When the House of Representatives impeached President Bill Clinton in 1998, his job approval ratings were north of 60 percent.