WASHINGTON -- Senate Republicans are scheduled to take up a key spending bill this week, but Democratic aides say they're getting signals that the GOP is rethinking its approach to the measure so the party can avoid uncomfortable votes on gun amendments that could come along with it.

In the wake of Sunday morning's mass shooting at a nightclub in Orlando, Florida, Democrats are renewing calls to bar people on the terrorism watch list from purchasing weapons of war, such as the AR-15 used in the massacre. Republicans have resisted the effort, warning that it is an unconstitutional abridgment of the Second Amendment.

Civil libertarians are also concerned about the precedent such a watch list-based policy would set, but the politics are becoming untenable for Republicans.

"I believe that our Republican colleagues, particularly so many of them now in a difficult political season, are going to find it very difficult," Sen. Chuck Schumer (D-N.Y.) said Monday in a conference call with reporters.

Democrats tried after the mass shooting last year in San Bernardino, California, to bar people on the watch list from buying guns, just as domestic abusers, felons and several other categories of people are proscribed. The attempt to pass the amendment authored by Sen. Dianne Feinstein (D-Calif.) failed on a nearly party-line vote.

Schumer said the shooting in Orlando may change some minds.

"Unfortunately, circumstances are going to force them to see the light, and not just bow in obeisance to the [National Rifle Association], whose positions on this issue are just simply extreme," he said.

Feinstein pointed to a recent study that determined 91 percent of the people on the terrorism watch list were able to buy weapons and said the easy access to guns was a draw for would-be killers.

"Without doing this, without making the change, we're just asking people to come into this country and go out and buy a gun," she said.

The spending bill coming up this week is the Commerce, Justice, Science and Related Agencies Appropriations bill, which would be a germane vehicle to try to load up with gun amendments, since it involves the Department of Justice. Democrats would first try to attach the watch-list measure, Schumer said. Other measures are also possible, such as background check improvements and assault weapons bans.

Since a vote to start the bill is already scheduled, Senate rules may have boxed in Majority Leader Mitch McConnell (R-Ky.), leaving him no way to pull the bill. He filed last week to hold a cloture vote to start considering the CJS bill on the floor Tuesday, which means he would likely need unanimous consent to withdraw it, something Democrats wouldn't grant.

There's still plenty of room for McConnell to maneuver to avoid gun votes. He could conceivably "fill the tree," which refers to a parliamentary procedure that blocks any new amendments from being considered.

He could also embrace the votes and try to offer counters, as he did last year when Democrats offered the same measure after the San Bernardino attack. Then, Sen. John Cornyn (R-Texas) offered a competing bill that would only stop a sale to someone on a watch list for 72 hours, and would require a judge to find probable cause to make the prohibition permanent.

The brittleness of the GOP's political position was laid bare by an incoherent Wall Street Journal editorial published Monday and titled "Jihad in Orlando." In it, the paper suggests the FBI didn't have enough information on Orlando suspect Omar Mateen to stop him from purchasing his weapon, but did have enough to set up an elaborate "sting" operation to try to trick him into planning a fake terror attack.

Offered the Journal (emphasis added):

"But one conclusion we’d draw is that the FBI is right to use “sting” operations against Americans who show jihadist leanings on social media or with friends. One way to stop a Mateen before he strikes is to have an undercover agent invite him to take a step toward violence. If he refuses, then he is probably not a threat. If he accepts, then it’s fair to conclude he might have acted on his own eventually. [...] A federal official disclosed that Mateen bought his weapons legally in recent days, and no doubt Democrats will make much of this politically in the coming days. But if the FBI doesn’t identify someone as a terror threat, then basic rights can’t be denied. Mateen was also a licensed security guard, and a determined jihadist will always be able to find firearms."

Feinstein argued that her measure could apply to a suspect like Mateen because it relies on a determination by the attorney general, not just a name on a watch list.

She pointed to a section of the bill that says:

“The Attorney General may deny a license application if the Attorney General determines that the applicant (including any responsible person) is known (or appropriately suspected) to be or have been engaged in conduct constituting, in preparation for, in aid of, or related to terrorism, or providing material support or resources for terrorism, and the Attorney General has a reasonable belief that the applicant may use a firearm in connection with terrorism.”

A spokesman for McConnell did not say what the leader's response would be.