WASHINGTON — Congress remains deeply skeptical of the landmark deal announced Tuesday to halt Iran’s nuclear ambitions, but lawmakers are unlikely to have the votes to stop it. While Democrats largely back President Barack Obama’s pursuit of an agreement to lift sanctions on Iran in return for measures to prevent the country from building nuclear weapons, Republicans who have the majority in both the House and Senate say the administration should walk away from a deal they fear concedes too much. “We knew from the beginning that any deal negotiated by the Obama administration would not go far enough to keep Iran from acquiring a nuclear weapon, or protect Israel from a nuclear Iran,” U.S. Rep. Doug Collins (R-Ga.) said.