There is no more passionate and principled advocate for greater military spending than Senator John McCain, so we wonder if the Arizona Republican appreciates that he recently voted to guarantee weaker U.S. defenses. To wit, his vote to kill health reform means that entitlements like Medicaid will continue to squeeze the Pentagon like an ever-tightening vise long after he has retired.

Many in Congress have lamented that President Trump’s budget proposal for fiscal 2018 is more modest than the military buildup he promised...