yes
No
The President is the head of the executive branch and IS the executive branch. This is why when he gives an order, it is called an executive order.
No. His presidency won't be in effect until the inauguration.
Marriage law is within the jurisdiction of the States and, therefore, such an action would be a State matter.
unknown
The current President Obama made an agreement with the Iraq which the Senate would be very unlikely to confirm. Treaties must confirmed by the Senate, so he opted for an executive order.
An Executive Order of the President can last indefinitely. However, the next President in office can overturn or modify it.
An Executive Order comes from the President. Laws are passed by Congress.
Strong opposition from opponents in Congress
Executive. The President can issue a pardon with an executive order.
None. Executive orders are not secret: in fact, in our internet age, few things are secret. The executive orders the president has signed are public information, and are posted to the White House website for anyone to see. And it is also a myth that Mr. Obama has signed more executive orders than anyone. In fact, in the year 2012, he has only signed 37 of them, and none are particularly controversial or shocking. The total for his entire presidency is about 140; President Bush issued nearly 300 during his term in office, and Bill Clinton issued more than 360 of them. I enclose a link to President Obama's executive orders, so you can see them for yourself. You are maybe confusing Executive Orders with Security Findings. A "finding" is often secret, and can be anything, up to and including an order to shoot a Predator missile at someone's car. Interestingly, President Ford (Republican) issued executive order #11905 prohibiting anyone in U.S. intelligence (like the CIA, who controls the Predator missiles) from carrying out assassinations, and President Carter (Democrat) issued executive order #12036, which extended and clarified the prohibition. No-one seemed to care about these when the CIA was recently ordered to use a Predator missile to kill Anwar al-Awlaki (an American citizen born in Cruces, New Mexico in 1971). Addendum: Not all Executive Orders are public information and indeed "ARE" Secret if deemed appropriate by the President. Many people believe President Obama overlooked the US Constitution is his fervor to make changes he deemed appropriate. However, separation of the Powers was not understood by Obama very apparently.
Probably not. First, it depends on what is in the executive order, but it is doubtful that any such order will fit the definition of "high crimes and misdemeanors" or be an example of treason. It is also not clear that the president will sign a "gun control" order. While he does want to reinstate the assault weapons ban or the ban against clips that hold 30 bullets (and some polls indicate the public agrees), there is little evidence that Mr. Obama plans to impose a broad ban on guns. That said, the gun issue is very contentious, and as a result, no matter what the president does, one side or the other will be upset. But the fact remains that presidents sign executive orders all the time, and as a former professor of constitutional law, it is doubtful that President Obama would sign any order that violated the constitution.