No one understands especially voters from the left or moderate voters how Trump has managed to sustain such loyalty with his strong Republican base. Some of the reasons why Trump does so well with his base is that he said what he would do if placed in office and he has kept his word; at least most of his promises. He promised to crack down on illegal immigration; build a wall and have Mexico pay for it, which he couldn't do. Instead, taxpayers are paying for the way; Trump passed a tax plan that helps corporations and the rich; eliminated tax deductions for regular taxpayers that they got less back on their annual tax refunds; Trump's base will rationalize that he cut payroll taxes so they got more in their paychecks even if it's not a great difference. Trump promised to eliminate Obamacare and is currently in the supreme court trying to overturn it. Trump promised to pack federal courts with conservative judges which he has along with Mc Connell. On the surface, it looks like he kept his promises to his base.
Secondly, the power of celebrity, his base has seen Trump as a successful businessman on the apprentice for ten years. They believe in his success despite his record of bankruptcies. Trump is good at media manipulation.
Thirdly, the scapegoating of immigrants for job loss when in reality Andrew Yang accurately described the issues of automation and technology taking over manufacturing and lower-level skilled jobs over.
Fourth, conservative media especially Fox News and talk radio which promotes false and propaganda for the white house. Half the country is being fed false narratives and pro-White House propaganda to fuel his popularity.
Fifth, fueling mistrust and doubt in traditional media so when the media accurately reports on what the administration does; they can dispute and cast doubt on the facts to the American public.
Sixth, Trump speaks in plain English and doesn't speak in political speaking terms that confuse constituents like other politicians. Trump is himself and makes no apology for it and I think his base admires that he doesn't try to change or modify himself for political expediency.