WASHINGTON, DC - FEBRUARY 04: U.S. Senate Majority Leader Sen. Mitch McConnell (R-KY) arrives at the U.S. Capitol February 4, 2019 in Washington, DC. The Senate is schedule to vote on the "Strengthening America's Security In The Middle East Act" today.  (Photo by Alex Wong/Getty Images)
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WASHINGTON, DC - FEBRUARY 04: U.S. Senate Majority Leader Sen. Mitch McConnell (R-KY) arrives at the U.S. Capitol February 4, 2019 in Washington, DC. The Senate is schedule to vote on the "Strengthening America's Security In The Middle East Act" today. (Photo by Alex Wong/Getty Images)
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(CNN) —  

In the struggle between Republican Senate Majority Leader Mitch McConnell and the Democratic-controlled House, the immovable object may finally have met an irresistible force.

McConnell has been the immovable object: He’s frustrated House Democrats by systematically blocking Senate votes so far on the lengthening list of bills they have passed, from gun control to additional protections for patients with preexisting health problems.

RELATED: Murkowski joins McConnell’s opposition to election security proposals, setting up clash with House

But McConnell’s blockade faces a new challenge as the House turns to a series of bills meant to fight foreign interference in the 2020 election. Those measures, aimed at defending fundamental American institutions from foreign subversion, may be tougher for the Kentucky Republican to portray as partisan overreach than the bills the House has passed so far. And that could make them an irresistible force that strains his overall strategy of preventing action on any House legislation.

“It could be the thing that has the public home in on where the problem is, where the obstruction is,” says Democratic Rep. John Sarbanes of Maryland, a leading author of the House election security agenda. “The public, and I understand that, they paint everything with a broad brush and they say Washington is dysfunctional. Here’s a case study that they are going to be very interested in, that shows … the problem is not with Washington, the problem is not broadly with Congress, the problem is with Mitch McConnell, who will not bring any of these things to the Senate floor.”

McConnell’s decision to methodically bar consideration of any of the House priorities already looms as a defining gamble in the GOP’s effort to maintain its Senate majority in next year’s election. He has leaned into his role as obstacle, portraying a Republican-controlled Senate as the last line of defense against a Democratic “socialist agenda” and calling himself the “Grim Reaper” for their legislative plans.

“I am indeed the ‘Grim Reaper’ when it comes to the socialist agenda that they have been ginning up over the House with overwhelming Democratic support, and sending it over to America,” he declared in an interview on Fox News Channel last week. “Things that would turn us into a country we have never been.” McConnell’s campaign is even providing contributors with T-shirts featuring a tombstone for “socialism” on the front and a similar quote underscoring his determination to block the House agenda on the back.

The electoral impact of McConnell’s strategy will likely be determined by which side successfully defines the agenda he is obstructing.

In making his case, McConnell focuses on the priorities of the House Democrats’ left wing, particularly the Green New Deal and a government-funded single-payer health care system.

“He talks about that almost every opportunity he can,” says Josh Holmes, McConnell’s former chief of staff. “Being in opposition to health care plans that end private health insurance or environmental deals that basically shut down your electricity provider is something that he’s pretty comfortable with.”

But neither single-payer health care nor the Green New Deal, which Republicans are confident they can paint as unprecedented government intrusion into the economy, is likely to reach a vote on the House floor, much less pass the chamber, before 2020.

Instead, the legislation the House has passed this year – and that McConnell is blocking – has focused more on expressions of social values and bread-and-butter economic concerns, like buttressing the Affordable Care Act and confronting high prescription drug costs. Many of these measures enjoy preponderant support from the public in polls.

Popular legislation stalled

The House, for instance, in early June passed legislation that provides legal status for potentially millions of “Dreamers,” young people brought to the country illegally as children. In a Fox News poll released Sunday, nearly three-fourths of Americans said they supported legal status for those young people.

In May, the House passed the “Equality Act,” which would bar discrimination in housing and employment based on sexual orientation or gender identity. An April poll from the nonpartisan Public Religion Research Institute likewise found that nearly three-fourths of Americans support legislation to ban such discrimination.

Also in May, the House passed legislation to block regulatory actions by the Trump administration that would dilute the Affordable Care Act’s protections for patients with preexisting medical problems. In April polling by the nonpartisan Kaiser Family Foundation, about two-thirds of Americans said it was important that health insurers be required to sell coverage to consumers with preexisting health conditions and be prevented from charging them more.

Polls have registered the most emphatic public support for legislation the House passed in February to require universal background checks for all gun sales. In a national Quinnipiac University poll earlier this year, an astounding 93% of Americans, including 89% of Republicans and 87% of gun owners, said they supported such a requirement.

Other House-passed measures this year include the Violence Against Women Act, legislation promoting greater gender equity in pay and comprehensive legislation to expand voting rights and impose new ethics guidelines on Washington. Senior Democratic House aides are confident that by the 2020 election, they will also pass legislation creating a nationwide $15 minimum wage, expanding the subsidies for families to purchase health insurance through the ACA’s exchanges, updating the Voting Rights Act and combating the rising costs of prescription drugs.

The strong public support for most of these ideas has Democrats cautiously optimistic that their challengers next year can portray incumbent Republican senators as part of a “do-nothing Senate” blocking action on important concerns.

“When your occupation is to vote every day down the line against things that matter to voters … sure, we are going to make those a significant issue,” says J.B. Poersch, president of Senate Majority PAC, a leading Democratic super PAC.

Democrats have been frustrated so far by their inability to create more pressure on McConnell to take up any of the House-passed bills; House Speaker Nancy Pelosi held a news conference last week where she brandished a chart showing “McConnell’s graveyard” of bills that he had blocked, complete with miniature tombstones.

Holmes, now president of a Washington communications firm, says House Democrats today face the same unforgiving equation Republicans did in 2013-14. During that congressional session, the GOP-controlled House passed a series of conservative priorities, only to see them systematically blocked by the Democratic majority led by then-Sen. Harry Reid of Nevada. Despite loud complaints, House Republicans could never generate enough pressure on Reid to force him to allow votes on the GOP plans.

McConnell feels politically secure bottling up the House priorities, Holmes says, “for the same reason Harry Reid didn’t feel particularly moved by the fact that (then-Speaker) John Boehner had moved every conservative bill dealing with the economy or social issues possible. The priorities of Nancy Pelosi are not the priorities of Mitch McConnell, period. And he’s very comfortable with that.”

Election security measures

Election security, though, could be an issue that causes at least some GOP senators to question McConnell’s blockade. Sarbanes, who chaired the House Democrats’ Democracy Reform Task Force, says the party plans to pass by August “a suite” of bills to safeguard the 2020 election against foreign interference.