It's not unusual for a sitting president to command 90% plus or receive 90% plus from his own party. Trump, Obama, G.W. Bush, Bill Clinton, G.H.W. Bush, Reagan, etc all averaged over 90% from their own party while president. G.W. Bush slipped quite a lot in the last year of his presidency down to just a 71% approval from his party, but his 94% for his first seven years kept his average above 90%. Bill Clinton was the opposite, averaging only 83% approval from his own party for his first two years, but averaged well above 90% for his last six to bring his two term average up to 91%
What's different with Trump is the attachment his supporters still have for him after he left the presidency. But Obama, G.W. Bill Clinton, G.H.W. Reagan all left the presidency and went into oblivion more or less. They didn't just fade away, but basically dropped off the viewing screen completely the day after they left office. With Trump, he's been the headliner on all news from the 21st of Jan on. He hasn't faded, let alone dropped off the screen. He still hogs it.
I think his supporters think the second impeachment was completely wrong and holding a trial in the senate after he become a private citizen was even more wrong. They've circled their wagons around Trump. It's could be a case of Trump, he's family, we'll protect him and destroy his enemies who tried to destroy him for no reason or the only reason they went after him was the R behind his name. He did nothing wrong outside of beating Hillary Clinton which the Democrats couldn't stand. So the democrats went for revenge. Call it a modern day feud.
I do think as long as Trump continues to be headline news, his followers will continue their devotion to him. This has been so weird, Trump has gotten much more news times, much more face time on the news, always the number one story, the headliner, the news has been all about Trump, but very little to nothing on Biden who just happens to be president these days.