What is an executive order? And how do US President Donald Trump's stack up?

President Trump's first week in office has been marked by two things: Controversy (over things like his inaugural crowd size and voter fraud accusations), and executive orders.

The first is old hat for Trump. But for casual observers - and even some political junkies who are paying close attention to Trump's policy moves - the second might be a little foreign. Trump signed two more executive orders yesterday, attempting to fulfill his promise of "extreme vetting" to keep potential "radial Islamic terorrists" out of the United States.

So what is an executive action or executive order? And how unusual is what Trump is doing with them?

Below, an explainer.

What is an executive order?

It falls under the broader umbrella of "executive actions" which derive their power from Article II of the Constitution, and it is the most formal executive action. Executive actions also include presidential memoranda (which are a step below executive orders and basically outline the administration's position on a policy issue), proclamations and directives.Basically, an executive order is an official statement from the president about how the federal agencies he oversees are to use their resources.

An executive order is not the president creating new law or appropriating new money from the US Treasury - both things that are the domain of Congress; it is the president instructing the government how it is to work within the parameters that are already set by Congress and the Constitution.

Trump's executive order on building a border wall, for example, basically establishes building the wall as a federal priority and directs the Department of Homeland Security to use already-available funding to get the ball rolling on its construction.

The president's executive orders are recorded in the Federal Register and are considered binding, but they are subject to legal review. (More on that next).

How can a president do this?

In a word: Carefully. Executive orders have often been the subject of controversy, with the opposition party accusing the president of over-stepping his authority and acting like a dictator. Basically, they're arguing that he's changing the law rather than working within it.

This came up most recently after President Obama signed executive orders exempting the children of illegal immigrants and parents of legal children from deportation. There were known as Deferred Action for Childhood Arrivals - or DACA - and Deferred Action for Parents of Americans and Lawful Permanent Residents - or DAPA.

The plans would shield about 4 million undocumented immigrants from deportation, but Republican governors and attorneys general have sued, alleging that Obama was essentially implementing immigration reform on his own - overstepping his authority. In June, the Supreme Court deadlocked, leaving a federal judge's ruling blocking the programs in place.

And questions have already arisen about he legality of an early Trump executive order involved illegal immigration: His order denying federal funding the sanctuary cities. Expect a court fight there, too.

President Donald Trump has been signing executive orders all week. Photo / AP

What is the history of executive orders?

They have been around for as long as we've had presidents, in fact - all the way back to George Washington.

Some of the more most historically significant - whether for good or ill - include:

• The Emancipation Proclamation (Abraham Lincoln)

• The suspension of habeas corpus during the Civil War (Lincoln)

• Sending federal troops to integrate Little Rock, Ark., schools (Dwight Eisenhower)

• The internment of Japanese-Americans (Franklin Roosevelt)

• The desegregation of the Armed Forces (Harry Truman)

How do Trump's number and scope of executive orders compare, historically?

While Trump's first days in office have seemed to be full of executive actions, that's not really all that uncommon. A new president often shows up with many directives for the agencies he takes oversight of.

Back in 2009, for example, President Obama signed nine executive orders in his first 10 days and 16 total in January and February.

Trump is under that curve so far. Through his first seven days, he has signed six executive orders (along with eight memoranda and one proclamation).

Of course, many executive orders can be pretty mundane; the true measure is how far he goes with his orders. That's a measurement that's both subjective and subject to legal review. To judge for yourself, see the orders and memoranda for yourself here.

Trump's executive orders prior to Friday - the border wall, sanctuary cities, beginning the repeal of Obamacare and expediting the Keystone XL pipeline - rankled Democrats who disagree with those policies. And that is even more the case with Friday's executive orders, which Democrats have argued amount to a thinly veiled ban on Muslim immigrants and refugees.

Whether any of them overstep Trump's authority or the spirit of the Constitution, though, is a debate that will occur in the coming weeks and months.

What are the political advantages and disadvantages of executive orders?

Executive actions are sometimes derogatorily referred to as "legislating by executive order" - basically, what a president does when Congress won't comply with his wishes.

That's not always the case - especially on more minor executive orders - but often, it is. Obama's executive orders on immigration, for example, came after years of failed attempts at comprehensive immigration reform, and Obama cited those failures when pitching the need for executive action that even he once suggested were beyond his authority. And any president would rather have Congress's stamp of approval on something controversial like that.

The political downside to executive orders, then, basically boils down to two things: 1) Getting struck down by the courts, and 2) Looking like you can't pass your agenda through Congress and are acting as an all-powerful executive - in a system designed to limit such absolute power.

The upside is, of course, that you can try to do it all by yourself, with just the stroke of a pen. (And then hope for the best.)