By Patricia Zengerle WASHINGTON (Reuters) -Forty-nine of the 50 Republican U.S. senators said on Monday they will not back an emerging new nuclear deal between Iran and world powers, underscoring their party’s opposition to attempts to revive a 2015 accord amid fears talks might collapse. Citing press reports about the as-yet-unfinalized agreement, which could be torpedoed by Russian opposition, the lawmakers said in a statement that Democratic President Joe Biden’s administration might reach a deal to weaken sanctions and lessen restrictions on Iran’s nuclear program. They pledged to do every…