Donald Trump has been the most persistently unpopular first-term president in the postwar era. Much of the nation is exhausted and embarrassed by his presidency, pining for normalcy, eager to change the channel. The president’s own internal polls show Mr. Trump trailing the former vice president, Joe Biden, not only in many battleground states Mr. Trump won in 2016, but in traditional Republican strongholds like Georgia.

But as we saw Tuesday night, during a huge, raucous rally in Orlando, Fla., Trump is viewed by his supporters almost as a demigod. One excited Trump supporter who was there told me he was overwhelmed by the unwavering support for Mr. Trump, driven by a sense that Mr. Trump has been deeply wronged — by the Mueller investigation, by the media and by what he described as “anti-Trump forces.” He also told me, based on conversations he had with others at the rally, that Mr. Trump’s supporters believe his era is “spiritually driven.” What he meant by that is that person after person reported that when it comes to Mr. Trump and the presidency, “God has chosen him and is protecting him.” It is the Children of Light against the Children of Darkness.

That certainly aligns with my sense of how Trump supporters see things. It’s not just that Mr. Trump is exceedingly popular among Republicans, with his approval rating this year hovering in the high 80s and low 90s. It is that he has won their undying loyalty and affection. As a Republican friend of mine put it to me recently, Mr. Trump is the general leading the army into battle against an enemy that needs to be vanquished for the good of the nation. When facing an existential threat, there is no room for public dissent. In Mr. Trump’s Republican Party, you are expected to treat him with reverence, submission and obeisance, or you will be treated as a traitor to king and cause. Just ask Jeff Flake, Bob Corker, Mark Sanford and Justin Amash.

It was unthinkable when Donald Trump rode down the escalator at Trump Tower four years ago to announce his improbable run for the presidency, but his imprint on the Republican Party is at least as large as that of Ronald Reagan’s at a comparable point in his presidency. The Republican Party has been transformed by Mr. Trump.