Democrats seem to appreciate that this is a problem. You saw this at the convention, where the hours before 6 p.m. — when most people weren’t watching — were heavy on praise for immigration and appearances by illegal immigrants who spoke movingly of their plight. But at the hour when the nation turned its eyes to the television, the paeans in favor of illegal migrants became dramatically more restrained.

Yet instead of solving this problem, Democrats opted to mostly speak in vague generalities and to avoid concrete questions: What percentage of our society should be foreign born? How should we choose the people we allow to migrate? Instead of formulating a clear policy, they relied on institutional inertia and lax enforcement to swell the foreign-born population to nearly 15 percent of the country. And Republicans, whose donor class likes generous immigration rules, were happy to go along.

That was fine as long as those groups were in charge of the status quo. Once Trump took over, however, that became infeasible. Trump, and anti-immigration Republicans in Congress, are going to be pushing specific policies to step up enforcement against people who are here illegally, and otherwise curtail legal immigration; a bill is already on the table that would sharply cut the number of people who can immigrate legally.

Successfully opposing these moves will require more than saying “He called Mexicans rapists!” Nor will it suffice to repeat how swell immigrants are.