President Barack Obama continued to urge Republicans to help pass an updated arms treaty between the United States and Russia, saying it would be the right thing to do for the nation.

Obama lobbied senators by phone Monday, in an effort to gain support for the New START treaty. The deal would significantly reduce the number of nuclear arms held by both countries.

The agreement is one of the biggest foreign and defense policy changes for the U.S. in the past 50 years.

"Ratifying a treaty like START isn't about winning a victory for an administration or a political party," Obama said. "It's about the safety and security of the United States of America."

Most Republicans feel the New START deal is flawed.

"I think the verification provisions are inadequate," Minority Leader Sen. Mitch McConnell, said. "And I do worry about the missile defense implications of it."

GOP leaders believe the treaty would limit the United States' ability to protect from ballistic missile attacks in the region.

Democrats need at least 67 votes to pass the New START deal. They expect to get 57 votes from their caucus. At least four Republicans have said they'll favor the deal.