Senate Majority Leader Mitch McConnell (R-KY) rejected President Donald Trump’s call to partially fund the border wall with a simple majority vote on Friday, suggesting not enough Senate Republicans support the measure.

President Trump called on McConnell to use the “nuclear option,” or switch to a simple majority vote in the Senate, to pass the continuing resolution (CR) that would partially fund the border wall. The House passed a CR last night that would fund $5.7 billion in border security.

“Mitch, use the Nuclear Option and get it done!” Trump wrote on Twitter. “Our Country is counting on you!”

Mitch, use the Nuclear Option and get it done! Our Country is counting on you! — Donald J. Trump (@realDonaldTrump) December 21, 2018

McConnell spokesman David Popp released a statement on Friday, contending that the Majority Leader continues to oppose going to a simple majority, or 51 votes, to partially fund the border wall. Popp said not enough Senate Republicans support the measure.

Popp said:

The Leader has said for years that the votes are not there in the Conference to use the nuclear option. Just this morning, several senators put out statements confirming their opposition, and confirming that there is not a majority in the conference to go down that road.

Retiring Sens. Jeff Flake (R-AZ), Orrin Hatch (R-UT), and Lamar Alexander (R-TN) all released statements on Friday, opposing the nuclear option to fund the wall.

“We have rules to follow. I want to put a stop to this practice of the Senate breaking its rules to change its rules,” Alexander said. “I will not vote to turn the Senate into a rule-breaking institution, and I hope that my colleagues will not.”

Not all Senate Republicans agree with the three retiring GOP lawmakers.

Sen. Steve Daines (R-MT) tweeted after the House passed its spending bill with wall funding that the Senate can do the same if it went to a simple majority. Daines noted that McConnell went “nuclear” to confirm judges through Congress’ upper chamber.

“House just passed a bill that fully funds government and enables @realDonaldTrump to secure our border/build the wall. Senate can do same by eliminating the filibuster,” Daines charged. “51 votes, same as we do for judges!”

House just passed a bill that fully funds government and enables @realDonaldTrump to secure our border/build the wall. Senate can do same by eliminating the filibuster. 51 votes, same as we do for judges! — Steve Daines (@SteveDaines) December 21, 2018

Conservative Review senior editor Daniel Horowitz suggested that Republicans can use arcane parliamentary procedures in the Senate to pass border wall funding with a simple majority, skipping the option of entirely “going nuclear.”

Horowitz said that Republicans can exploit Senate Rule XIX, otherwise known as the “the two-speech rule,” which would prevent individual senators from speaking “more than twice upon any one question in debate on the same legislative day.” In other words, this would force Democrats to continually fillibuster throughout the same “legislative day” and eventually exhaust Senate Democrats.

The Conservative Review editor explained:

Given that Republicans preside over the chair and control the floor, they can refuse to officially adjourn, opting only to recess temporarily, and keep the Senate in the same legislative day indefinitely. This will ensure that even the Democrats who are willing and able to speak for a long time will eventually be forced to relent. This never happens and is never enforced, because Republicans never force Democrats to hold the floor in the first place and McConnell simply won’t bring up legislation without a unanimous consent agreement or without 60 votes to ultimately shut off debate. But if he forced the minority to hold the floor and enforced Rule XIX, Democrats would exhaust themselves very quickly. This is a strategy laid out by James Wallner, an expert on Senate procedure who is currently completing a manuscript on the history of the Senate. Wallner points out that Democrats do have the ability to challenge rulings of the chair and bring up points of order or call for quorum calls as means of prolonging their floor time, but Republicans can dispense with their motions with 51 votes. Eventually, Democrats would run out of steam and exhaust their two speeches per member. This would theoretically take several days or weeks, but it all depends on the determination of each side. If Republicans keep them in session day and night and over the weekends and make them hold the floor, Democrats would eventually run out of options to block a majority vote to proceed with the border wall funding continuing resolution.

Horowitz suggested that the “optics” of forcing Democrats to hold the floor “will make the Democrat-speech givers look like fools and obstructionists during Christmas.”

The editor said that these sort of hardball tactics enabled Democrats to pass the civil rights bills in the 1960’s.

Horowitz added, “Republicans with convictions should recognize that having sovereign borders is the civil rights issue for all Americans, rooted in the entire social compact underpinning our federal government.”

“Trump must remember that his entire presidency is on the line. This is his moment,” Horowitz charged. “He must use the bully pulpit and every constitutional tool at his disposal to finally force a national debate over the integrity of our own borders.”