Democrats are giving Senate Republicans a taste of their own medicine.

The new minority is pulling out all the stops to stymie Sen. Mitch McConnell’s first bill as majority leader — legislation to approve the Keystone XL pipeline, which faces a veto threat from President Barack Obama.

And in a possible sign of trouble to come for the Kentucky Republican, Democrats are having some success — even though plenty of their own members support the pipeline. A vote to end debate on the legislation failed on Monday afternoon, 53-39, falling short of the 60 votes required to defeat a filibuster.

In an extraordinary act of trolling, Democrats seized on McConnell’s promise of an open amendment process to clog up the legislation with more than 150 amendments, and then complained that McConnell tried to “shut down debate” by attempting to move to a final vote on Monday.

McConnell’s office observes that he allowed 24 amendments — many of them from Democrats — to come up on the Keystone bill, more than former Senate Majority Leader Harry Reid permitted in the entire year of 2014.

But Democrats persisted — and then persisted some more.

Sen. Barbara Boxer (CA) offered an amendment to address the impact of oil spills on public health. Sens. Maria Cantwell (WA) and Bob Menendez (NJ) offered one to protect private property in the building of the pipeline. Sen. Ben Cardin (MD) offered another to protect communities from pipeline-related hazards that could affect their drinking water. Sens. Debbie Stabenow (MI) and Gary Peters (MI) offered one to study the environmental impact on the Great Lakes.

And so on.

When McConnell attempted to move forward to a final vote, Senate Minority Whip Dick Durbin objected, saying the Republican leader had “purged the calendar of five of the six Democratic amendments.”

Reid’s spokesman Adam Jentleson said, “Sen. McConnell is offering a variety of excuses for shutting down debate on Keystone despite the fact that senators are still seeking votes.”

Democrats went on to complete their first filibuster of the 114th Congress, with just four defections: Sens. Michael Bennet (CO), Joe Donnelly (IN), Heidi Heitkamp and Joe Manchin (WV). Numerous Democrats who support the pipeline and voted to approve it last month supported the Monday filibuster.

Senate Republican leaders were clearly frustrated.

“It was surprising to see a handful of Democrats use a ‘lack of amendments’ as a rationale for filibustering a bipartisan bill that they voted for just two months ago, despite Sen. Reid giving them NO amendments,” Don Stewart, McConnell’s top spokesman, said in an email.

The Democrats’ unity can be rivaled only by McConnell’s own successes at making their lives miserable during eight years in the majority, with escalated filibusters and creative stalling tactics. It came despite the absence of Reid from the Capitol, who has spent most of the month working from his Washington home at the Ritz-Carlton as he nurses a recent injury to his right eye, in which doctors aren’t sure he’ll ever recover his vision.

Monday’s vote does not bode well for McConnell. If he’s unable to secure Democratic support to move legislation, he won’t be able to get much done, even when it comes to mundane messaging bills. Complicating his challenge will be that several of his members — Sens. Rand Paul (KY), Ted Cruz (TX) and Marco Rubio (FL) — may run for president, which would force them to miss some votes while they’re on the campaign trail.

McConnell proceeded to bring up the bill again on Tuesday morning, saying that “the vote last night to filibuster was disappointing” and calling on Democrats to reconsider.