I?ll try to answer in general terms because to get too specific would require a lot of writing.
Back in the FDR era, we had two major problems inflicted on us: The unconstitutional federal regulatory bureaucracy and another set of laws collectively known as the "War and Emergency Powers Act." These are entwined significantly. So, today, everyone in Washington knows that the federal government is tromping all over all of our so called "unalienable" rights guaranteed by the Constitution. Both the Senate and the House had very enlightening hearings on this problem a few years ago.
After a 1973 Senate Church Committee hearing, the preamble to the report let off with the words: "A majority of the people of the United States have lived all their lives under emergency rule. For 40 years, freedoms and governmental procedures guaranteed by the Constitution have, in varying degrees, been abridged by laws brought into force by states of national emergency."
It gets better, though. The Senate committee had the Attorney General testify and they grilled him about this. The Attorney General stated: "This vast range of powers, taken together, confer enough authority to rule the country without reference to normal constitutional processes. Under the powers delegated by these statutes, the President may: seize property; organize and control the means of production; seize commodities; assign military forces abroad; institute martial law; seize and control all transportation and communications; regulate the operation of private enterprises; restrict travel; and, in a plethora of particular ways, control the lives of all American citizens."
As Senator Church commented in the same document (Senate Report 93-549 of 1973): "If the President can create crimes by fiat and without congressional approval, our system is not much different from that of the Communists, which allegedly threatens our existence. These powers, if exercised, would confer upon the President total authority to do anything he pleased."
The problem was, Congress had already been using some of those very same unconstitutional laws to create other unconstitutional law for 40 years!
Justice Thomas is the only member of the Supreme Court to address this problem since 1936. But, one out of nine doesn't help much.
Now . . . as to why the Justice Department asked the Court to not hear Emerson; that's easy. Historically, Government seldom wants the Court to hear a case that could overturn federal law. That's about all there is to that.
Because, once the Court gets the case, it could have the opportunity to overturn many such laws. It all depends on how narrowly or widely the majority opinion is written. Five Justices with a burr up their asses about a topic could overturn 50 years of law Justice thought was written in stone. So, they never want the Court to hear such a case.
And, by the way, the Court has already signaled -- repeatedly -- that it is willing to reexamine federal law on interstate commerce and those associated laws (which includes gun laws). They are just looking for the right case. Is Emerson it? I don't know.
Some background on this can be found at: http://209.15.142.23/reports/headsup/state98.htm That text came about after one of Clinton's State of the Union speeches that got me off on a major rant. Later, it became a book outline, but I never found an agent willing to handle it. The material was just too hot back then.
-- Yep, we've had several discussions over the years about the Church Commission findings, & if memory serves, your articles have sparked more than one of them. -- Thanks again for your comments here, & the threads initial article.
-- Sheds much light on why the administration is trying to prevent Emerson from being taken before the USSC.