I’ve got a better policy than dumbass Pat Buchanan -
1. Selection of immigrants. Accept those who can pass a battery of tests - intelligence, health, aptitude.
2. Selection of sources - preferential immigration from populations known to be easily assimilated, such as East Asia, Europe, India.
It’s illegal immigration that is completely ruining America today. As for legal immigration, there are plenty of checks and balances, especially on the financial front, that the consular office in the origin-country scrutinizes carefully. You can verify this by going to any foreign US consulate website, and reading the complex procedure for immigration.
With the illegals, however, the entire mechanism is destroyed. Even the lottery system for specific African countries, aids this.