Washington — President Trump is pressuring Iran to either curtail its nuclear program or face potential military strikes, grappling with an issue that has vexed presidents from both parties for decades. Iran — which denies any nuclear weapons ambitions — has amassed a growing stockpile of uranium that is enriched to near the level of purity necessary to build a bomb. Mr. Trump ordered strikes on a trio of key Iranian nuclear sites last June, but now, less than a year later, the president has