(CNN) - Republican Sen. Pat Toomey of Pennsylvania blamed political polarization for the failure of last month's background check compromise he reached with Democratic Sen. Joe Manchin, saying some in his party simply voted against the measure to prevent the president from winning a legislative victory.
"In the end, it didn't pass because we're so politicized. There were some on my side who did not want to be seen helping the president do something he wanted to get done, just because the president wanted to do it," Toomey said.
"The toughest thing to do in politics is to do the right thing when your supporters think the right thing is something else," he added.
His comments came in an interview Tuesday with a roundtable of Digital First Media editors in the offices of the Times Herald newspaper in Norristown, Pennsylvania.
According to the editors at the meeting, Toomey clarified his comment, saying he meant to say Republicans in general, not just his GOP colleagues in the Senate.
Toomey was one of four Republicans who voted on a measure to expand the background check system so that it covers private sales at gun shows and online. Five Democrats voted against the proposal (including Senate Majority Leader Harry Reid, who voted no so he could bring the bill back up later).
In a 54-46 vote, the measure failed to reach the 60 votes needed to move forward in the Senate. Along with the background checks legislation, a ban on assault weapons also went down in defeat.
President Barack Obama said Tuesday in a news conference that he suspected there were Republican members in Congress who vote against their instincts for political purposes.
"Their base thinks that compromise with me is somehow a betrayal. They're worried about primaries. And I understand all that. And we're going to try to do everything we can to create a permission structure for them to be able to do what's going to be best for the country," he said. "But it's going to take some time."
The president and gun control advocates chided lawmakers for failing to pass the proposal, the only one that had a real shot of passing among the slew of gun proposals brought forward in the wake of the elementary school massacre in Newtown, Connecticut.
While Obama, Reid and gun control groups have vowed to keep up the pressure and bring the legislation back for a vote down the road, Toomey expressed doubt that a second vote will happen soon.
"Reid could bring it up for a vote at any time, but we need five people to change their minds," Toomey said.
"It's a pretty heavy lift to get five senators to change their mind on a big issue like this," he added. "It's not likely to happen any time soon. I hope people will reconsider over time."
His comments sounded less enthusiastic compared with those made by Manchin. The senator from West Virginia said Sunday he believes the measure is still alive and together they can persuade enough lawmakers to support it.
"I truly believe if we have time to sell the bill, and people read the bill," it will gain support, Manchin said. "I'm willing to go anywhere in this country, I'm going to debate anybody on this issue, read the bill and you tell me what you don't like."
– CNN's Kevin Liptak contributed to this report.