A federal judge Friday quickly moved to block President Trump’s effort to ban Harvard University from enrolling international students and revoke their visas. District Court Judge Allison Burroughs ruled that Harvard made a “sufficient showing” that it would be hurt by the administration’s effort to revoke its certification to host foreign students, potentially ousting up to 7,000 students and financially crippling the prestigious Ivy League institution. “It will sustain immediate and irreparable harm before all parties have an opportunity to be heard,” Burroughs wrote in a terse two-page order. The lightning-quick ruling came just hours after Harvard sued to prevent...