"He's been working with both sides to try to get the strongest bill we can that has enforceable background checks," White House senior adviser Dan Pfeiffer said Sunday on ABC's "This Week."
Other Obama gun control priorities include banning assault weapons and ammunition magazines with more than 10 rounds. Both bans are expected to be offered as amendments when Senate debate begins, but the assault weapons ban seems sure to be defeated and the high-capacity magazine prohibition also faces difficult odds.
For weeks, Manchin has been part of an effort to craft a background check compromise, along with Sens. Chuck Schumer, D-N.Y., and Mark Kirk, R-Ill. Schumer focused his efforts on conservative Sen. Tom Coburn, R-Okla., but those talks sputtered over Schumer's insistence on -- and Coburn's opposition to -- requiring that records be kept of private gun sales.
"I'm still hopeful that what I call the sweet spot -- background checks -- can succeed," Schumer said Sunday. "We're working hard there."
Proponents say background checks and records -- which are currently retained by gun dealers, not the government -- are the best way to ensure that would-be gun-buyers' histories are researched. Opponents say the system is a step toward government files on gun owners and say criminals routinely skirt the checks anyway.
Asked about the potential compromise, Manchin spokesman Jonathan Kott said, "My boss continues to talk to all of his colleagues."
Toomey spokeswoman E.R. Anderson said she could provide no information.
Sen. John McCain, R-Ariz., urged fellow Republicans to allow debate to go forward without a filibuster, even as he declined to express support for a background check bill.
"The purpose of the United States Senate is to debate and to vote and to let the people know where we stand," McCain said, appearing alongside Schumer on CBS'<!p><#148>Face the Nation."
With or without an agreement, the Senate gun legislation would toughen federal laws against illegal firearms sales, including against straw purchasers, those who buy firearms for criminals or others barred from owning them. The legislation also would provide $40 million a year, a modest increase from current levels of $30 million, for a federal program that helps schools take safety measures such as reinforcing classroom doors.
In addition, the gun bill contains language by Schumer expand background checks to cover nearly all gun transactions, with narrow exceptions that include sales involving immediate relatives. Even without a bipartisan deal, Schumer is expected to expand the exemptions to more relatives, people with permits to carry concealed weapons and others.