Gregory Korte

USA TODAY

WASHINGTON — The last time the Senate held votes on gun legislation was last December, a day after husband-and-wife shooters killed 14 people in San Bernardino.

All four proposals were defeated.

Before that, the occasion was the Sandy Hook Elementary shooting that killed 20 children and six teachers, which inspired gun control proposals in 2013. Those failed, too.

It's become a pattern: Mass shooting incident, followed by gun control proposals and unsuccessful Senate votes.

Now, after the biggest mass shooting in U.S. history in Orlando a week ago, Democrats are hoping for a breakthrough when the Senate holds four more votes Monday.

Republicans, too, are showing some movement. With the support of the National Rifle Association, they've proposed an amendment that would allow law enforcement to block a firearm sale for national security reasons in narrow circumstances.

The proposals scheduled for a vote Monday — all as amendments to a Justice Department spending bill — include:

► An amendment by Sen. Dianne Feinstein, D-Calif., would allow the attorney general to deny a gun sale to anyone if she has a "reasonable belief" — a lesser standard than "probable cause" — that the buyer was likely to engage in terrorism. The proposal is popularly known as the "no-fly, no-buy" amendment, but wouldn't just apply to people on the "no fly" terrorist watch list.

► An Republican alternative by Sen. John Cornyn, R-Texas, which would require that law enforcement be alerted when anyone on the terror watch list attempts to buy a weapon from a licensed dealer. If the buyer has been investigated for terrorism within the past five years, the attorney general could block a sale for up to three days while a court reviews the sale.

► An amendment by Sen. Chuck Grassley, R-Iowa, would make it more difficult to add mentally ill people to the background check database, giving people suspected of serious mental illness a process to challenge that determination.

► An amendment by Sen. Chris Murphy, D-Conn., that would close the "gun show loophole" by requiring every gun purchaser to undergo a background check, and to expand the background check database.

It was Murphy's 15-hour talk-a-thon on the Senate floor last week that pressured Senate Republicans to allow the series of votes. But Murphy conceded Sunday that he's unlikely to succeed — in part because he needs 60 votes to break a threatened Republican filibuster.

Democratic senators stage 'filibuster' to demand action on gun bills

"I admit that the background checks bill is going to be tough to get 60 votes on, but we still have hope that we can get Republicans to support the bill, stopping terrorists from getting weapons," Murphy told ABC's This Week on Sunday. "But in the final analysis, what may be most important is that our filibuster helped galvanize an entire country around this issue."

More likely to pass is the Cornyn amendment, a Republican-backed measure which has been endorsed explicitly by the National Rifle Association and implicitly by the presumed GOP presidential nominee, Donald Trump.

Senate Majority Leader Mitch McConnell, R-Ky., suggested last week that the Cornyn proposal — which also calls for the detention of terrorists if a judge finds probable cause — is the best response to the Orlando incident. “Of course no one wants terrorists to be able to buy guns. Let’s get real here," he said last week. "So if Democrats are actually serious about getting a solution on that issue, not just making a political talking point, they’ll join with us."

Feinstein argued Sunday that Cornyn's "probable cause" standard is too high. "So that would cut out a lot of people who are probable threats," she said on CBS's Face the Nation. "And it has to be completed within three days, which Justice and others tell us is impossible to complete the process within three days."

In one sign of how important the vote is to election-year politics, Sen. Bernie Sanders, I-Vt, is expected to cast his first Senate votes since January. “As the recent tragedy in Orlando has made crystal clear, we must ban the sale and distribution of assault weapons, end the gun show loophole and expand instant background checks,” he said last week.

Bernie Sanders to return to Senate for gun vote

And what if all the proposals fail? The White House says there are no more executive orders under consideration, and that all eyes were on the Senate action. "I truly hope that senators rise to the moment and do the right thing," Obama said in Orlando last week. "I hope that senators who voted no on background checks after Newtown have a change of heart."