Sen. Chris MurphyChristopher (Chris) Scott MurphyDems mull big changes after Brazile bombshell After Texas shooting, lawmakers question whether military has systemic reporting problem Warren to GOP: Thoughts and prayers not enough after Texas shooting MORE (D-Conn.) and other Democrats have taken over the Senate floor to call for tougher gun control laws and specifically action on keeping people on terrorist watchlists from buying firearms.

“I'm prepared to stand on this floor and talk about the need for this body to come together on keeping terrorists away from getting guns ... for, frankly, as long as I can, because I know that we can come together on this issue,” Murphy said in beginning the filibuster on Wednesday.

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Murphy began speaking at about 11:20 a.m., and the filibuster was still going more than 12 hours later.

Other Democrats who joined him included Sens. Richard Blumenthal (Conn.), Joe ManchinJoseph (Joe) ManchinDems mull big changes after Brazile bombshell A bipartisan bridge opens between the House and Senate Collins, Manchin to serve as No Labels co-chairs MORE (W.Va.), Patrick LeahyPatrick Joseph LeahyMaxine Waters to Sessions: 'Time to go back to the plantation' Franken has 'a lot of questions' for Sessions on Russia contacts Senate Dems demand Sessions testify after Papadopoulos plea deal MORE (Vt.), Al FrankenAlan (Al) Stuart FrankenOvernight Tech: Senate panel subpoenaed ex-Yahoo chief | Twitter gives all users 280 characters | FBI can't access Texas shooter's phone | EU wants tax answers from Apple Week ahead: DHS nominee heads before Senate | Ex-Yahoo chief to testify on hack | Senators dig into election security Feinstein: Sessions should re-testify on Russia meetings MORE (Minn.), Cory Booker (N.J.), Bill NelsonClarence (Bill) William NelsonOvernight Tech: Senate panel subpoenaed ex-Yahoo chief | Twitter gives all users 280 characters | FBI can't access Texas shooter's phone | EU wants tax answers from Apple Overnight Cybersecurity: What we learned from Carter Page's House Intel testimony | House to mark up foreign intel reform law | FBI can't access Texas shooter's phone | Sessions to testify at hearing amid Russia scrutiny Former Yahoo CEO subpoenaed to appear before Congress MORE (Fla.), Dick DurbinRichard (Dick) Joseph DurbinDems mull big changes after Brazile bombshell After Texas shooting, lawmakers question whether military has systemic reporting problem Bipartisan group of lawmakers aim to reform US sugar program MORE (Ill.), Charles SchumerCharles (Chuck) Ellis SchumerTrump is right: The visa lotto has got to go Schumer predicts bipartisan support for passing DACA fix this year No room for amnesty in our government spending bill MORE (N.Y.), Ben CardinBenjamin (Ben) Louis CardinFacebook farce shows lawmaker deviousness, demagoguery Dem senator wants details on Manafort's multiple passports US backs out of global oil anti-corruption effort MORE (Md.) and Ed MarkeyEdward (Ed) John MarkeyCBS series 'Madam Secretary' exploring 'fake news' plot Senate Dems warn against cutting ObamaCare fund to pay for children's health program Trump’s North Korea strategy requires an intervention from Congress MORE (Mass.).

It also won support from presumptive Democatic presidential nominee Hillary ClintonHillary Diane Rodham ClintonGOP rushes to cut ties to Moore Papadopoulos was in regular contact with Stephen Miller, helped edit Trump speech: report Bannon jokes Clinton got her ‘ass kicked’ in 2016 election MORE and her rival, Sen. Bernie SandersBernard (Bernie) SandersWorld leaders reach agreement on trade deal without United States: report Sanders on Brazile revelations: DNC needs ‘far more transparency’ Sen. Warren sold out the DNC MORE (I-Vt.).

The Senate is currently considering an appropriations bill for the Commerce and Justice departments and science programs. Though no votes are currently scheduled, the senators are blocking any amendments to the bill.

"I don't think we should proceed with debate on amendments to this bill until we have figured out a way to come together," Murphy said, referring to the spending bill.

The Democrats are also technically blocking Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellMcConnell expects Paul to return to Senate next week Former Hill staff calls for mandatory harassment training Gaming the odds of any GOP tax bill getting signed into law MORE (R-Ky.) from ending debate on the legislation, though a spokesman shot down any speculation that the Republican leader would have tried to wrap up work on the spending bill Wednesday.

Democrats have given no indication how long they plan to hold the Senate floor. Chris Harris, a spokesman for Murphy, said Democrats launched the talkathon because the senator will no longer accept “inaction or half measures in the face of continued slaughter.”

The effort comes three days after the deadliest mass shooting in U.S. history. A gunman armed with a Sig Sauer MCX rifle and a handgun on early Sunday killed 49 people at an Orlando nightclub. 

Murphy is well-known for his support for tougher gun control laws. One of America's most shocking gun crimes occurred in his home state in Newtown, where 20 children and six adults were shot to death at Sandy Hook Elementary School.

"I can't tell you how hard it is to look into the eyes of the families of those little boys and girls who were killed in Sandy Hook and tell them that almost four years later we've done nothing, nothing at all," Murphy said. 

Since the Orlando attack, Democrats have put a renewed focused on legislation meant to block the sale of guns to people on terrorist watchlists. 

An effort to move legislation was previously blocked last year. 

Sen. Ben Sasse (Neb.) was the first Republican senator to join Murphy and other Democrats, asking a question about the government's terror watchlists.

"I'm familiar with the terrorist screening database. There are a series of lists that fall from the database, but I don't think there's any such thing as 'the terrorist watchlist,' and I certainly don't understand what due process rights would apply," Sasse said.

Sasse's comment reflects a central problem Republicans have with a proposal from Sen. Dianne FeinsteinDianne Emiel FeinsteinSenators push mandatory sexual harassment training for members, staff Bipartisan group of lawmakers aim to reform US sugar program Senate panel to hold hearing on bump stocks MORE (D-Calif.) that would give the attorney general broad authority to block people on watchlists from being able to buy guns or explosives. 

Republicans argue that could deny constitutional rights to Americans who aren’t actually tied to terrorism.

Instead, Sasse and most Republicans support an alternative proposal by Sen. John CornynJohn CornynAfter Texas shooting, lawmakers question whether military has systemic reporting problem Overnight Defense: Lawmakers question military's lapse after Texas shooting | Trump asks North Korea to 'make a deal' | Senate panel approves Army pick Overnight Regulation: House passes bill to overturn joint-employer rule | Trump officials to allow work requirements for Medicaid | Lawmakers 'alarmed' by EPA's science board changes MORE (R-Texas) that would allow the attorney general to delay suspected terrorists from getting a gun for up to 72 hours while seeking a court order to stop the sale.

Sen. Pat Toomey (R-Pa.), who faces a tough reelection bid, came to the Senate floor urging his colleagues to compromise. 
 
"There's an obvious opportunity here, guys, to work together and find the solution," he said. "What I'm suggesting is let's get to work here." 
 
Toomey on Wednesday criticized the Feinstein measure as "badly flawed." But he also said that Cornyn's proposal, which he previously voted for, likely didn't give enough leeway to the attorney general. 
 
He made the comments after Democratic Senate candidate Katie McGinty, who is hoping to unseat Toomey, pressured the GOP senator to back the Feinstein legislation during a press conference Tuesday. 
 
Wednesday afternoon, Toomey said he planned to introduce a compromise bill Thursday aimed at combining aspects of both the Feinstein and Cornyn proposals.
 
Toomey's legislation would require the attorney general to create a list of "likely terrorists" that could be blocked from buying guns. The list would then be submitted to the Foreign Intelligence Surveillance Court, which would review it annually and remove any Americans inadvertently included, according to a summary of the forthcoming bill from his office.

Updated at 11:35 p.m.