Donald Trump is entering his second term with vows to cut a vast array of government services and a radical plan to do so. Rather than relying on his party’s control of Congress to trim the budget, Trump and his advisers intend to test an obscure legal theory holding that presidents have sweeping power to withhold funding from programs they dislike. His plan, known as “impoundment,” threatens to provoke a major clash over the limits of the president’s control over the budget. The Constitution gives Congress the sole authority to appropriate the federal budget, while the role of the executive branch is to dole out the money effectively. But Trump and his advisers are asserting that a president can unilaterally ignore Congress’ spending decisions and “impound” funds if he opposes them or deems them wasteful. Trump’s designs on the budget are part of his administration’s larger plan to consolidate as much power in the executive branch as possible. Trump spokespeople did not respond to ...