Last night, Saturday Night Live's "cold open" mocked President Obama's new executive action shielding 4 million illegal immigrants from the threat of immediate deportation. To the tune of a "Schoolhouse Rock!" song, Kenan Thompson dresses up as a "Bill" and explains how Congress passes one. Until Jay Pharoah, playing Obama, pushes Thompson down the Capitol steps.

"There's actually an even easier way to get things done around here, and it's called an executive order," Obama (Pharoah) says. Bobby Moynihan shows up dressed as an Executive Order and sings, "I'm an executive order, and I pretty much just happen."

The Bill (Thompson) climbs back up the stairs and declares, "Look at the midterm elections. People clearly don't want this."

Obama is asked whether this is constitutional. "Of course," he says. "Presidents issue executive orders all the time." Then the Executive Order (Moynihan) starts singing, "I'll create a new national park ... or a new highway," and, keeping with the rhythm, the president adds, "or bring legal status to 5 million undocument[ed] immigrants."

The Executive Order then looks at himself and shouts ,"Oh my God! I didn't have time to read myself. Woah!"

This skit got a couple of things right, and a couple of things wrong. For starters, Obama didn't sign an executive order. He is taking executive action, in particular by directing the Department of Homeland Security to expand programs that defer deportation for classes of undocumented immigrants — parents of U.S. citizens or permanent-resident children, as well as undocumented immigrants brought to the country as children.

See a handy flow chart to determine who qualifies.

Obama's action on Thursday adds 4 million new eligible immigrants, on top of the 1 million young immigrants who became eligible for deferred deportation under Obama's original 2012 program.

The cold open got the basic explanation of what the difference is between a law and executive order right. And SNL also is correct that more Americans, even if they support comprehensive immigration reform, don't believe Obama should do it by fiat.

As to whether the executive action is unconstitutional? That's a matter of debate, of course. Some House Republicans think so and may add a complaint to a suit they are planning to file challenging Obama's executive actions on his health-care law.

One Obama backer who also supports a comprehensive overhaul of immigration laws says the action may be impeachable, as "by constitutional design, impeachment for 'treason, bribery, or other high crimes and misdemeanors' is a political accusation."

The best case may come from Republican governors and state attorneys general, who say that the actions will put new burdens on their local governments and that, thus, they may have the most legal "standing" to sue. Kansas's secretary of state, Kris Kobach, is one of them and is profiled in Sunday's Washington Post.

All that said, many legal experts are dubious about the success of a constitutional or legal challenge. Indeed, Obama benefits from considerable precedent: Presidents George H.W. Bush and Ronald Reagan used their authorities to extend protection to illegal immigrants.

According to the Justice Department memo spelling out Obama's legal authority, the president is drawing a careful line. He is protecting the parents of citizens and permanent residents — people who could conceivably have a right to become citizens in the future given they are the family of lawful permanent residents or citizens.

Meanwhile,  young immigrants brought to the United States as children had no say in their parents' decision to violate U.S. immigration law. Notably, the parents of these "dreamers," as advocates call them," are not protected under Obama's action, unless they also have children who are citizens and permanent residents.  From the Justice memo:

Many provisions of the [Immigration and Nationality Act] reflect Congress’s general concern with not separating individuals who are legally entitled to live in the United States from their immediate family members. ... But the immigration laws do not express comparable concern for uniting persons who lack lawful status (or prospective lawful status) in the United States with their families.

Obama's measure still goes far beyond his predecessors, who shielded anywhere from 100,000 to 1.5 million people from deportations. If there is a court challenge, it would, in any event, go on for years, perhaps into the next president's term.

And so what matters most for Obama's action is public opinion, and what his successor does. The SNL skit, in that sense, doesn't help him.