There’s a reason Republicans from Reagan to Bush supported reasonably open immigration policies. They are and have always been good for America.

A new summary of the research from the National Academies of Sciences, Engineering and Medicine found that immigrants are integrating into society as well as ever. The bulk of the evidence shows that immigrants have a hugely positive effect on total American G.D.P. while having little effect on overall wages. The surge in Asian immigration will bring a gigantic number of highly skilled people, who end up with higher education levels than the American average, higher productivity levels and higher incomes.

So why is the Trump message selling? Well, economic growth has been slow and wages have been stagnant (mostly because technology is displacing workers). Government is dysfunctional and the immigration issue has become a symbol for how elites are out of touch with the mainstream.

But mostly it’s the clash of two trends: the graying of the G.O.P. and the browning of America. The Republican primary base is more and more made up of older people, who have significantly more negative views about immigration. Second, by 2044, America will be a majority-minority country. This is a very different America than the one people who grew up in the 1960s were used to. It’s a historical transformation that is bound to raise very legitimate concerns.

The way for Republicans to address these concerns, though, is not to build a wall and treat immigrants as suspicious alien invaders. It’s to work on our legal immigration system — make the system ample and streamlined enough so that most people come here in the right way, in a way they can be vetted.

Admit more skilled immigrants and fewer unskilled ones. This would be a giant boon to the economy over all. It would make our immigration policies less geared to serving the elites — giving them ample supplies of nannies and nail polishers. Reducing the supply of unskilled immigrants may do something to raise the wages of unskilled natives and ease their legitimate concerns.

Donald Trump’s G.O.P. is a rear-window party pining for a white America that is never coming back. Ronald Reagan’s G.O.P., and maybe some future G.O.P., will fix the immigration system and attract the people who will make the country innovative, dynamic and interesting for decades to come.