To be clear, the two problems—the decline and the scandals—are different matters. The scandals have not been linked directly to the president. They are vexing to the administration, but they are not the source of its current impotence. Instead, Mr. Obama’s power and influence have been sapped as a direct result of his own choices and decisions. He also suffers from shortcomings normal to a second term, such as a new, less able team of advisers and cabinet members and the arrogance fed by an impressive re-election.

In his first term, when Democrats controlled the House and Senate, Mr. Obama ignored Republicans—he didn’t need their votes to pass the $800 billion stimulus, the Affordable Care Act (aka ObamaCare) and Dodd-Frank, with its fresh wave of Wall Street regulations. Then, after Republicans captured the House in the 2010 midterm election, his efforts to reach agreements with them proved futile.

Why did Mr. Obama fail at compromise? For one thing, he is rarely able to mask his contempt for Republicans, especially those with conservative views. For another, he began to question Republicans’ motives, insisting publicly that their paramount goal in Washington is to protect the rich from higher taxes. As a tactic for encouraging compromise, his approach was counterproductive.

Robert Merry, the editor of the National Interest magazine and a longtime Washington journalist, recently pinpointed a bigger reason for the impasse after 2010: “It is a deadlock born largely of the president’s resolve to push an agenda for which he has no clear national consensus.” In other words, Mr. Obama is too liberal to find common ground with Republicans. The spending cuts he offers are illusory, the tax increases specific.