WASHINGTON -- An agreement between the United States and Russia to slash their nuclear arsenals was in danger of collapse after an influential Republican senator said Tuesday it should not be voted on this year.With a terse statement, Sen. Jon Kyl dealt a major setback to President Barack Obama's efforts to improve ties with Russia and to his broader strategy for reducing nuclear arms worldwide. The treaty, known as New START, had been seen as one of Obama's top foreign policy accomplishments.