The Senate, divided over how to respond to the nation’s latest mass shooting, will vote Monday on four measures supporters say would keep guns out of the hands of terrorists.

All of them have failed in political show votes after previous massacres. All need 60 votes to pass, an enormous hurdle — especially in an overheated election season on a topic on which compromise is hard to find.

The proposals:

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– Democrats are lining up behind a measure by Sen. Dianne Feinstein, D-Calif., that would give the government broad authority to block gun sales to people who have been subject to terrorism investigations in the past five years.

Such people would be flagged during the gun background check. The government could then veto the sale if the Justice Department decides there is a “reasonable suspicion” that the buyer has become involved in terrorism or is preparing to do so. Anyone who gets denied could appeal.

Such a law might have prevented Orlando gunman Omar Mateen from buying the two weapons he used in the attack. Mateen was investigated in 2013 and 2014 for possible terrorism links, but had been cleared by the FBI and was not on any lists when he purchased a Sig Sauer MCX semiautomatic assault rifle and a Glock handgun.

Feinstein’s proposal was defeated in December after the terrorist attack in San Bernardino, Calif. It received only 45 of the needed 60 votes, with only one Republican, Mark Kirk of Illinois, crossing over to vote in support. The White House is now on board but Republican minds aren’t changing.

– The Republican alternative is a proposal by Sen. John Cornyn of Texas. He wants a 72-hour delay when anyone who has been on a federal terrorism watch list in the past five years tries to buy a gun.

To block the purchase, prosecutors would have to go to court within the 72-hour window and convince a judge that there is “probable cause” that the individual would use the weapon in connection with terrorism.

Cornyn’s proposal also was defeated after the San Bernadino shooting in December.

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Cornyn got 55 out of the 60 votes needed to pass, and there’s no sign that he’s picked up more votes since, with Democrats arguing the proposal wouldn’t do much of anything to keep terrorists from getting guns.

– Republicans, led by Sens. Charles Grassley, R-Iowa, and Ted Cruz, R-Texas, will get a vote on a plan to bolster federal databases to make it easier to notify law enforcement agencies if someone under investigation as a terrorist in recent years tries to buy a firearm.

They would also make it easier for mental health records to be added to the database. Previous similar efforts have failed.

– Democrats will get a vote Monday on a broader proposal. It would require, with only a few exceptions, that background checks be undertaken for any transfer or sale of a gun, including at gun shows and online. Similar legislation has failed before, notably in April, 2013, four months after 20 children and six adults were shot to death at an elementary school in Newtown, Conn. There’s little expectation that this time around is going to be different.

So the betting is that the Senate once again will take no action to stop terrorists from getting guns.

The one hope for compromise comes from Sen. Susan Collins, R-Maine, who is hoping to win support to stop the sale of guns to people who are on the government’s no-fly list or on a separate list that triggers extra screening at the airport known as the selectee list.

Those lists are narrower than the federal database the Democrats are focused on, the Terrorist Screening Database, which is compiled by the FBI from its records as well as those of the CIA and other intelligence agencies. According to government reports, the list contains hundreds of thousands of names.

In contrast, the no-fly list is thought to contain about 47,000 names. The size of the selectee list is unknown.

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