Really, it's about how Obama got not just his own party but progressives as well as centrists back on his side.
EJ Dionne writes in the Washington Post:
In a superb reconstruction of why the president decided to move on his own, Washington Post reporters Juliet Eilperin, Ed O’Keefe and David Nakamura note that the last straw for Obama was House Speaker John Boehner’s refusal to say after the election that he would bring up an immigration bill if the president agreed to postpone executive action. In the absence of concrete pledges that something would get done, there was no point in waiting any longer.
All this explains the jubilation among progressives. They not only agree with the substance of what Obama did but also see him as finally calling his opponents’ bluff. He has forced the contradictions of the Republican establishmentarians into the sunlight. ...WaPo
The Republicans have tried to have it both ways. They've failed.
For the six years since Obama’s election to the presidency, the Republican right has been on offense, continually blurring those distinctions between the “factual” and the “perceptual.” They keep charging that Obama is a dangerous radical even when he pursues middle-of-the-road policies. Their supposedly more temperate colleagues go along because they don’t have to pay a price.
Obama has just told them their free ride is over. The stakes in American politics will be much clearer because he did. ...WaPo