With Elon Musk rummaging through the executive branch and advising that President Trump should unilaterally shut down agencies and halt day-to-day operations, Republicans are playing defense for the world’s richest man even as it’s unclear he can make any kind of lasting change at the nation’s capital. After three weeks riding high, Mr. Musk is about to meet his greatest challenge — the Article I branch. 

Welcome to Washington, where the leader of the Department of Government Efficiency has seen nearly every one of his gains halted in federal court. A challenge to his buyout for federal employees will be heard today in Massachusetts. The funding freeze he wanted has been rescinded by the White House and blocked by a federal judge. The firing of more than 2,000 employees of the United States Agency for International Development has, similarly, been put on hold. 

Even as Mr. Musk’s blitz against federal agencies stalls, congressional Republicans are already failing to deliver him the significant cuts he is seeking. The GOP is preparing to begin the legislative session with a package aimed at funding border security and deportation operations, expansions of military capabilities and infrastructure, and a swath of new energy leases. 

The bill, written by Senator Graham, chairman of the Budget Committee, is revenue neutral. It will do nothing to pay down America’s debt nor achieve Mr. Musk’s dream of cutting at least $2 trillion from the budget. The world’s richest man has said he wants to slash the budget by nearly one-third, but has run into Mr. Trump’s campaign vow to avoid cutting Social Security or Medicare.

Even if Mr. Musk wanted to cut $2 trillion, he wouldn’t just run into Mr. Trump, but Congress, too. Slashing $2 trillion annually means ending all funding for the Pentagon and every other federal discretionary program, plus an extra $200 billion in entitlement spending. In short, he’s on track to either fail or go to the mat with Congress. He has already promised to fund a primary challenger to any Republican who votes against Mr. Trump’s stated position. 

For those who don’t follow the lesser-known power centers of Washington closely, the most influential persons you’ve never heard chair the 12 powerful House appropriations subcommittees. These are the 12 people who, in an ideal world, each pass their own specific spending bills before bringing each individual legislative item to the floor, though that hasn’t happened in years.

Even though the politics of Congress don’t allow for that regular order, the 12 chairmen are the experts in exactly when and how the federal government spends its money, and one of those lawmakers has said Mr. Musk’s plans for slashing government waste to the tune of several trillion dollars is unrealistic. 

“If they can find it, they can find it,” Congressman Mike Simpson, who is chairman of the environment and interior appropriations subcommittee, tells The New York Sun of the money conservatives are trying to cut. When asked if he thought Republicans could reach that goal, Mr. Simpson said, “I don’t.”

Like with all presidents of both parties, Messrs. Trump and Musk face a problem of math. The president has decided to take three House members to staff his administration — Congressman Mike Waltz, who is now national security advisor, Congresswoman Elise Stefanik, who will soon be ambassador to the United Nations, and Congressman Matt Gaetz, who resigned from Congress after being nominated for attorney general, only to withdraw eight days later.

Mr. Trump’s decision will soon leave him with a one-seat majority in the House, at a time when his administration is dangerously close to being the first in history to default on the national debt. Even when he is at full strength in a few months after three special elections likely deliver him additional GOP votes, Speaker Johnson will only be able to lose two members on a vote in order for it to be successful. 

If history is any guide, Republicans will more likely than not lose a significant number of House seats. On average, since 1982, presidents have lost 27 seats in their first midterm elections in the White House. To ask vulnerable and moderate Republicans to cut government spending at a rate not seen in the modern era will be a near-impossible lift.