Health care, Social Security, Medicare and other social programs are all on the chopping block as the Republican-led Congress scrambles to make up for the revenue lost to its planned tax cuts. The Pentagon, however, remains a sacred cow, destined to receive yet more money.

The military budget is now $643 billion. The actual and potential threats from Russia, China, North Korea and Islamic extremists are all serious, but giving the Pentagon another huge increase defies common sense. The Pentagon already wastes about one in five of the taxpayer dollars it receives, according to a Pentagon-commissioned study. And the United States, which has plenty of other urgent needs, already spends more on its military than the next seven countries combined.

The opening bid for the 2018 defense budget came from President Trump, who in May proposed $677 billion. That was $54 billion above a budget cap set by Congress in 2011, after the 2008 financial crisis led to demands for fiscal restraint. Then last month, Congress upped his ante by passing a 2018 military authorization bill that would increase spending to around $700 billion, some $85 billion above the legal cap. Mr. Trump signed that bill into law on Tuesday.

For the moment, that increase is a fiction. Before it can occur, Congress must remove the 2011 caps and appropriate the money. That is the focus of the present budget battle on Capitol Hill. Republican leaders reportedly want to increase military spending by at least Mr. Trump’s original figure of $54 billion and nonmilitary spending by $37 billion. Democratic leaders are insisting on equal increases for both categories.