WASHINGTON (AP) — A cornerstone of President Barack Obama's drive to check gun violence is gathering bipartisan steam as four senators, including two of the National Rifle Association's congressional champions, privately seek compromise on requiring far more firearms purchasers to undergo background checks.

The talks are being held even as Obama's call to ban assault weapons and high-capacity ammunition magazines, the two other major pillars of his plan, are hitting rough waters on Capitol Hill. An agreement among the four senators to expand background checks would add significant impetus to that high-profile proposal by getting the endorsement of a group that ranges from one of the Senate's most liberal Democrats to one of its most conservative Republicans.

"We'll get something, I hope. I'm praying for it," said Sen. Joe Manchin, D-W.Va., one of the participants.