The president was in a bind.
He wanted a "comprehensive" immigration bill to add to his list of accomplishments for many reasons. If he succeeded, he would do so where his predecessor had not. If he were successful, he would also establish himself, and the Democratic Party, as having delivered a legislative victory on a policy about which many Spanish-speaking immigrants care. Electoral gratitude would follow.
Yet, he was well aware that the 1986 Immigration and Reform Act (IRCA) had failed to deliver on its promise to dramatically reduce illegal migration to the United States. On the contrary, its passage preceded by just a few years the steady rise over time in the illegal alien population.
As a result, long-standing and deep skepticism developed regarding the government's ability or interest in putting into place serious enforcement laws and acting on them. This skepticism made any effort at comprehensive immigration legislation vulnerable.
When he first assume office, the president had the political numbers in Congress to pass an immigration bill to his liking, given that Democrats controlled both houses of Congress with minority-proof majorities.
The president, though, had larger ambitions than passing an immigration bill. The president wanted, he said several times, to "transform America".
A large part of that ambition was economic. He wanted to use government to ensure that those who he saw as not having had a fair opportunity for economic success got their chance while he was president. This involved expanding government's reach to ensure that those who wanted subsidized education, heath care, or home ownership aid would receive help through federal programs.
All of these programs were redistributive at their core. They took resources from those the president felt could afford to pay and used them to subsidize others who he felt couldn't or shouldn't.
The president's preferred immigration bill was also transformational. The Senate bill he favored would double legal immigration and, when combined with the amnesty, would grant 33 million green cards over 10 years. And many of those new immigrants would come from groups that had supported the president in his successful White House bid in 2008. He had every reason to expect that if he were able to pass immigration legislation that legalized those groups' friends, relatives, and fellow ethnic group members the president and the Democratic Party would stand to reap enormous electoral benefits down the road.
But before he was able to successfully argue for his preference for a "comprehensive" bill that would bring 11 or 12 million illegal aliens "out of the shadows", he had to convince skeptical Americans that his was not another IRCA redo in which legalization would precede serious enforcement efforts and set the stage 10 or 20 years down the road for another debilitating national debate about bringing a new group of millions of illegal aliens out of the shadows.
In short, the president had to demonstrate that he was tough on immigration enforcement so that he would be trusted when the inevitable criticisms arose about his championing a second major amnesty involving millions of illegal aliens.
To accomplish this purpose, the president chose a dual-track strategy that was paradoxical in its enforcement premises and thus ultimately unsuccessful as a political strategy once his tactics became clear.
He would be tough on (some) criminal illegal aliens, and supportive and accepting, to the extent that he could publicly be, to almost every other category of illegal aliens.
The first was meant to satisfy the public and almost succeeded, until the second undercut his credibility.