Barack Obama told his staff the day after he was inaugurated that "transparency and the rule of law" would be his presidency's "touchstones." In the case of Medicare, they haven't been.

Mr. Obama has ignored a law requiring he send Congress a plan to strengthen Medicare's finances—even though members of his own cabinet have reminded him in writing of his duty to do so.

Medicare was originally designed to be paid for mostly by special dedicated taxes. Yet it has become increasingly dependent on general revenues as expenses have far outrun both projections and Medicare tax receipts. By 2024, according to the annual report of the Medicare trustees, the hospital insurance trust fund will be exhausted.

To force Washington to take action before Medicare overwhelms the federal budget, fiscal experts wrote a presidential obligation into the Medicare Reform Act of 2003. Under that provision, if Medicare's trustees forecast that general revenues will be required for 45% or more of the program's outlays within a seven-year period, then the president must propose legislation to correct the problem within 15 days of his next budget submission. Congress then has to give the proposal expedited consideration.

In their annual report this spring, Medicare's trustees—who include four members of Mr. Obama's cabinet as well as two outside experts—said "the threshold was in fact breached" during the last fiscal year and "a Presidential proposal is required by law in response." As, indeed, one was required in 2010 as well. The Democratic majority waived the requirement during the last Congress, but it remains in force this year. The president has continued to ignore the law, failing to send Congress a plan to fix Medicare's finances.

Karl Rove is a former senior adviser and deputy chief of staff to President George W. Bush. He is a Fox News contributor and author of "Courage and Consequence" (Threshold Editions, 2010). To continue reading his column in The Wall Street Journal, click here.

Karl Rove joined Fox News Channel as a political contributor in February 2008. He also currently serves as a columnist for the Wall Street Journal. Mr. Rove helped organize the political-action committee American Crossroads. His latest book is "The Triumph of William McKinley: Why the Election of 1896 Still Matters" (Simon & Schuster, 2015). Follow him on Twitter @KarlRove.