WASHINGTON — (CNN) Senators couldn’t muster enough bipartisan support to pass a series of gun control measures Monday, the latest in a long string of failed attempts at enacting tighter curbs on firearms in the United States.

Spurred by the worst mass shooting in U.S. history, senators from each party introduced the measures they said would have strengthened background checks and prevented suspected terrorists from obtaining weapons.

But tough election year politics, paired with disputes over the effectiveness of each party’s ideas, proved too powerful to break the longstanding partisan gridlock that’s surrounded gun issues for years.

The result was expected.

A fifth option, set to be introduced Tuesday by moderate Republican Sen. Susan Collins, has generated more optimism, but still faces long odds at passage.

The measures Monday each went down in succession on largely party line votes.

The 60-vote threshold required for passage prevented even Republicans, who control the chamber, from pushing through their favored measures.

The Senate rejected first a Republican proposal to update the background check system for gun purchases, which would have required states to add more information on mental health records to a national database.

It also included a provision to alert law enforcement agencies when an individual who was on a government terror watch list in the last five years buys a gun.

The proposal, sponsored by Iowa GOP Sen. Chuck Grassley, failed to get the 60 votes for passage.

The vote was 53-47, largely along party lines.

Some Senate Democrats warned that the legislation’s revised definition of who would be considered mentally ill could potentially still allow those with significant psychological issues to legally purchase guns.

A second proposal to expand the background check system for those buying guns to require checks at gun shows and for online purchases went down 44-56.

Connecticut Democratic Sen. Chris Murphy, who launched a nearly 15-hour filibuster last week to press for new gun restrictions after the Orlando massacre where 49 people were killed, sponsored the proposal.

A Republican proposal to delay gun sales to individuals included on a government terror watch list failed in a mostly party-line vote of 53-47.

The measure was sponsored by Texas GOP Sen. John Cornyn.

The bill would allow a judge to permanently block a purchase if the court determined probable cause that the individual is involved in terrorist activity.

And a Democratic option that sought to bar all gun sales to those individuals on the terror watch list failed 47-53, the second time the proposal went down to defeat after a mass shooting.

California Democratic Sen. Dianne Feinstein originally pushed the proposal in December after a shooting in San Bernardino, and revived it after the horrific Orlando nightclub shooting by a gunman who pledged allegiance to the terror group ISIS.

Feinstein’s plan did garner the support of some Republicans, including Sen. Kelly Ayotte of New Hampshire who is facing a fierce re-election bid this year.

Sen. Mark Kirk, another vulnerable Republican up for re-election, voted with Democrats on all of the four amendments.

Ahead of the votes, both gun advocates and proponents of tighter restrictions sought to galvanize supporters.

“They’re blaming you, the (National Rifle Association) for the terrorist attack in Orlando and taking advantage of this tragedy to push their gun control agenda while emotions run high,” the NRA wrote to members Monday.

The group holds powerful sway among Republicans and moderate Democrats.

Senate Democratic Leader Harry Reid, meanwhile, blasted Republicans for withholding support for his party’s plans, saying on the Senate floor that “Senate Republicans should be embarrassed — but they are not, because the NRA is happy.”

Majority Leader Mitch McConnell touted the GOP proposals as more directly targeted toward the Orlando shooting, and argued the Democratic proposals would not provide due process for individuals barred from purchasing guns.

Before the first votes were cast, eyes were already turning to an effort by Collins to craft another gun control, one week after the Orlando terror attack.

The Maine lawmaker was expected to unveil her proposal on Tuesday.

“Theres tremendous interest on both sides of the aisle, I hope that will be having a press conference tomorrow,” Collins said on Monday. “We’ll see where we are.”

The Collins measure would bar people on the government’s no-fly list — a significantly smaller group than the terror watch list — from purchasing guns and also set in place some protections for anyone wrongly placed on the no-fly list.

The vast majority of Americans favor preventing those on terror watch lists from buying guns — including 90% of Republicans, according to a CNN/ORC poll released on Monday.

That’s a higher figure than either Democrats (85%) and Independents (83%) who say they support such a rule.

Cornyn said Monday that McConnell is open to Collins getting a vote on her gun control proposal.

“I congratulate her for her good work. I just think these are the first votes were going to have, but that doesn’t preclude other votes.

Sen. McConnell said if she wants a vote, I’m sure she could get one,” Cornyn — who introduced one of the four measures up for a vote Monday — said before voting began.

Collins’ proposal, however, has not garnered much support on the Democratic side.

Even if her gun control legislation does make its way out of the Senate, it’s unlikely to get a vote in the House, where House Speaker Paul Ryan threw cold water on the idea during his weekly press conference last Thursday.

Minnesota Sen. Amy Klobuchar told CNN’s Jim Sciutto that while there remains fierce resistance in the House — where Republicans outnumber Democrats 247-188 — the push for action in the wake of the Orlando terror attack reflects new momentum in the gun control debate.

“I don’t know that it’s going to be different than when we had votes in the past, but there is one thing that is different. People are starting to talk. There are starting to be negotiations going on. I think that’s very important,” Klobuchar said.