Unlike the heady days of the Bill Clinton era, the economy is no longer the overriding concern for most Americans. Now it’s immigration, stupid. Today, a new Gallup poll has found that immigration is, according to 28% of Americans, the most important problem, up eight percentage points in just the last month.

 With Joe Biden and Donald Trump due to visit different parts of the border on Thursday, both men are clearly aware of the political capital to be won (or lost) on the issue. While (we hope) there will be no tears on their visit a la AOC, there is certainly enough to make the incumbent president despondent: a separate question in the Gallup survey found a record-high 55% of Americans, up eight points from last year, said that “large numbers of immigrants entering the United States illegally” is a critical threat to US vital interests. The prior high was 50% in 2004. Matt Yglesias’ dream of one billion Americans may be coming true sooner rather than later…