America has the best universities in the world, but its immigration enforcers have done a good job of making them less attractive. The proportion of the world’s overseas students who come to America has fallen from 23% in 2000 to 18% in 2009. America educated 66% of the world’s MBAs in 2000; that share fell to 44% in 2011, and has shrivelled even in absolute terms, from 126,000 to 116,000. The biggest turn-off is the difficulty of obtaining a work visa after graduating—even highly-skilled foreigners typically wait a decade for a green card. President Barack Obama pays lip service to the need to open up, but has overseen millions of deportations. A new study from the Kauffman Foundation, a think-tank in Missouri, finds that anti-immigrant politics appear to have stunted American enterprise. The proportion of Silicon Valley startups with immigrant founders has tumbled from 52% to 44% since 2005.