What is your definition of "failed"? A businessman who has businesses that make a profit worldwide doesn't seem too "failed." His argument may have been at least partially valid in 2016 when he did not have a record to execute. Now it does. here it is.
What Trump has done in the last 3 years is to turn the economy into the strongest economy the country has seen in the last 15 years at least. He has faced difficult problems that other presidents kicked the can on the road for decades. This includes illegal immigration. It includes commercial problems with China, as well as problems with them in the field of American intellectual property. It has just promoted a new trade association of the United States, Canada and Mexico (USMCA), eliminating a number of problems with the old one (NAFTA). He has taken a very visible stance with the pro-life movement.
Conservative voters got fed up with politicians who forgot why they were elected when they went to Washington. They get caught up in politics, political minutiae and lose the courage to do what they think is right. Many conservative voters thought they saw something in Trump and thought he would not be prone to that. It turned out to be very correct, more than they ever thought. That's why Trump's support has only grown since 2016, even for those who are discouraged by their antics.
This is what Trump is running now. Not as he has done in the business world!