It may not be the biggest Supreme Court case in history, or even in the last century. But it will be a defining case which doesn't happen more than once or twice a generation.

For the next three days, the Supreme Court will listen to arguments regarding the Affordable Care Act, or Obamacare. At stake: How much can the Constitution be stretched to accomodate the "social justice" agenda of liberals?

The Hill:

The six-hour oral argument is the longest the court has heard in 45 years. And this is the first time in more than 75 years that the court is in a position to strike down a sitting president's agenda while he runs for reelection.

"It's just perfect, in terms of this being a first-term president's signature legislation, and that it could be invalidated during a presidential election year," said Carl Tobias, a law professor at the University of Richmond.

That last instance came in 1935 when, in President Franklin D. Roosevelt's first term, the court considered the constitutionality of his National Recovery Act and struck it down.

Eventually, FDR got tired of SCOTUS declaring many of his recovery schemes unconstitutional and tried to pack the court by expanding its size and allowing him to appoint several more justices. Even the president's Democratic colleagues rebelled at such a naked power play and his plan was defeated.

The political implications are enormous as well:

A ruling striking down all or part of the law would seem like a gift to Mitt Romney, the likely Republican nominee, who has struggled to draw a sharp contrast with Obama on healthcare.

On the other hand, a legal victory for "Obamacare" could energize conservative voters who aren't especially fired up about Romney. Rep. Allen West (R-Fla.), a Tea Party favorite, said a ruling in Obama's favor would be a "big blow" to principles of individual liberty.

"I think that a lot of people would be really pissed off, put it that way," West said when asked whether a decision upholding the mandate would energize the right.

Obama's supporters, though, see the healthcare case as a potential test for the Tea Party, whose deep anger over the healthcare law was central to Republicans' victories in 2010. If this court, with its usually conservative majority, upholds the mandate, the Tea Party's rhetoric about reclaiming the Constitution might not sound quite as powerful.

Most court watchers believe the mandate will be upheld along with the rest of Obamacare. The precedents favor that notion and the Supremes are usually reluctant to overturn the will of congress.

But the momentum of big government has been building for 80 years and derailing that train is going to take not only a more conservative court but a solid majority of conservatives in congress - for a generation or more.

A decision is expected some time in June.