Here is the gun control legislation passed in the House that Mitch McConnell refuses to take up in the Senate

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• When Senate Majority Leader Mitch McConnell tweeted on Sunday offering his support for law enforcement and thoughts and prayers for the victims of the El Paso mass shooting, social media users responded with a fierce online backlash. 
• Democrats and many Twitter users called for McConnell to take action to curb the epidemic of gun violence in America.
• Many pointed to a bill passed in February that would enact universal background checks for all gun purchases - it was the most sweeping legislation to pass the House in nearly a quarter century, but McConnell has stalled the bill in the Senate.
• Here are the gun control bills that the Republican-controlled Senate has not taken up under McConnell. 
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When Senate Majority Leader Mitch McConnell tweeted on Sunday offering both his support for law enforcement and thoughts and prayers for the victims of the El Paso mass shooting, social media users responded with a fierce backlash. 

Both users and Democrats called for McConnell to take action to curb the epidemic of gun violence in America in the wake of mass shootings in El Paso, Texas, and Dayton, Ohio that left 30 people dead over the weekend. Many pointed to a bill the House passed in February to enact universal background checks for all gun purchases - it was the most significant gun control legislation to pass that chamber since the federal assault weapons ban in 1994.

Senate Minority Leader Chuck Schumer, Democrat of New York, also called for McConnell to organize an immediate vote on gun control legislation the House already passed, tweeting, "gavel the Senate into emergency session to take immediate action on the bipartisan, House-passed universal background checks legislation."

Currently, McConnell placed that bill and another on the Senate calendar, instead of referring them to the appropriate committees where they could be debated before possibly receiving a floor vote - the move is a form of legislative limbo.

Read more: The US spends less on gun violence research than nearly every other leading cause of death in America - and that's on purpose

Here are the gun control bills that the Republican-controlled Senate has not taken up under McConnell. 

Bipartisan Background Checks Act of 2019 (H.R. 8)

The first major gun control bill that the House passed in over two decades, H.R. 8 would require universal background checks and close the loopholes for buyers at gun shows and private sellers online. It passed in February 240-190 in a mostly party-line vote, with eight Republicans joining almost every Democrat to vote for the bill.

Currently, only federally-licensed gun dealers have to complete background checks.

But the bill still makes space for exemptions, such as when a family member decides to gift a firearm to somebody else.

Enhanced Background Checks Act (H.R. 112)

This bill would extend the current background check review period from three days to ten. It's being sponsored by Rep. Jim Clyburn, a South Carolina Democrat who also serves as the House Majority Whip. The bill also passed 240-190.

What are the bills' legislative chances?

It's unlikely the bills would pass the Senate if McConnell puts both for a floor vote. Though universal background checks has overwhelming support among voters of both parties, congressional Republicans have historically voted against such legislation - and they're in control of the Senate. Republicans have opposed the bills, arguing they infringe on the rights of law-abiding citizens and would fail to curb gun violence. 

The National Rifle Association still wields substantial influence within Congress, pouring millions of dollars to lobby mostly Republican lawmakers over the last two years. But its legislative effectiveness isn't what it used to be as five of their top bills were not signed into law by President Donald Trump.  Internal power struggles in recent months have also hurt the group.

The last major push to reform the nation's gun laws came after the Newtown massacre that killed 20 children in Dec. 2012, when Democrats led a similar push to implement background checks on all gun purchases, along with banning assault weapons and high-capacity magazines. But after a wrenching debate, the bills failed to get the 60 votes necessary to bypass the filibuster in a Democratic-controlled Senate.

Would they be effective?

Republicans have said the bills would be ineffective in addressing gun violence. But Democrats and gun control activists contend that they would provide a blueprint for future efforts.

Democratic Rep. Mike Thompson pointed out that background checks stop 88,000 gun sales every year "to criminals, domestic abusers, individuals with dangerous mental illnesses or other prohibited purchasers." But under current law, they can still obtain firearms at gun shows or through private sales online.

In addition, a majority of the guns used in 19 recent mass shootings were bought legally after the gunman passed a federal background check, according to the New York Times. Nine of them had been documented to have mental health issues or criminal histories - and they were still able to buy their weapons.