Donald Trump ended his first week as president by signing an executive order that means citizens of Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen will not be allowed to enter the United States.

Although the travel ban is one of a series of measures aimed – according to Trump – at "protecting the nation from foreign terrorist entry", people have been quick to point out that there is no obvious correlation between the countries affected by the ban and actual attacks in the United States. For example, none of the 9/11 hijackers came from any of the seven designated countries and, according to figures covering a 40-year period up to the end of 2015, foreigners from the seven countries have not killed any Americans in terrorist attacks on US soil.

However, a careful reading of the executive order [text here] shows that Trump does not claim there is any correlation. Nor does he claim that the ban will directly reduce the chances of attacks. Instead, he offers an even weirder explanation: that the ban has been introduced for administrative convenience.

Trump's order begins with a preamble saying scrutiny of visa applications was tightened up after the 9/11 attacks but "these measures did not stop attacks by foreign nationals who were admitted to the United States".  It continues:

"Numerous foreign-born individuals have been convicted or implicated in terrorism-related crimes since September 11, 2001, including foreign nationals who entered the United States after receiving visitor, student, or employment visas, or who entered through the United States refugee resettlement program."

This appears to be another of Trump's exaggerations, based on figures circulated last year by Republican senator Jeff Sessions who is now Trump's nominee for the post of Attorney General. Sessions is a long-standing campaigner against refugees, claiming they pose a threat to national security.

Last June, a document produced by Sessions claimed that out of "at least 580 individuals convicted in terror cases since 9/11", at least 380 were foreign-born. The trick here lay mainly in Sessions' extremely broad view of what consituted a "terror case". Alex Nowrasteh, an immigration policy analyst, pulled the figures apart in an article for the Cato Institute (libertarian think-tank on the political right):

First, 241 of the convictions (42 percent) were not for terrorism offenses. Senator Sessions puffed his numbers by including “terrorism-related convictions,” a nebulous category that includes investigations that begin due to a terrorism tip but then end in non-terrorism convictions.  My favorite examples of this are the convictions of Nasser Abuali, Hussein Abuali, and Rabi Ahmed.  An informant told the FBI that the trio tried to purchase a rocket-propelled grenade launcher, but the FBI found no evidence supporting the accusation.  The three individuals were instead convicted of receiving two truckloads of stolen cereal.  That is a crime but it is not terrorism. 

Second, only 40 of the 580 convictions (6.9 percent) were for foreigners planning a terrorist attack on US soil.  Seeking to join a foreign terrorist group overseas, material support for a foreign terrorist, and seeking to commit an act of terror on foreign soil account for 180 of the 580 convictions (31 percent).  Terrorism on foreign soil is a crime, should be a crime, and those convicted of these offenses should be punished severely but the government cannot claim that these convictions made America safe again because these folks were not targeting US soil.

Third, 92 of the 580 convictions (16 percent) were for US born citizens.  No change in immigration law, visa limitations, or more rigorous security checks would have stopped them. 

Thus, Trump's executive order is based on a highly questionable premise and Nowrasteh says it "will have virtually no effect on improving US national security". Others argue that it may even make the US less safe, since it has given many ordinary Muslims a genuine grievance which jihadists will be eager to capitalise upon.

Although the travel ban is causing enormous disruption and appears to mean that tens of thousands who are living legally in the United States will not be allowed to return if they travel abroad, Trump presents it as incidental to the main purpose of his executive order, which is a wide-ranging review of visa procedures. The aim, it says, is "to prevent the admission of foreign nationals who intend to exploit United States immigration laws for malevolent purposes".

In a bizarre paragraph of the order (3c), Trump says the purpose of the travel ban is "to temporarily reduce investigative burdens on relevant agencies during the review period". He has therefore decided to "suspend" entry of "immigrants and non-immigrants" (i.e. everyone) from the seven designated countries for a period of 90 days.

However, as an explanation for the ban, this makes little sense. If the administrative "burden" is a real problem there would be no reason to block people from the designated countries who already have visas or have previously been approved for residence in the United States.

There has been much speculation about the choice of countries affected by the ban. Some have pointed out that the list omits several terrorism-prone countries where Trump has business interests, but the real explanation seems more straightforward. The seven countries – Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen – had previously been designated in connection with the American system that lets citizens of 38 countries travel to the US for short stays without a visa. Under the Visa Waiver Program Improvement and Terrorist Travel Prevention Act of 2015, anyone who happens to have visited any of the seven countries since the end of February 2011 is no longer entitled to a waiver and has to apply for a visa instead. (There are a few exceptions, e.g. for officials travelling on government business.)

Adopting the same list may be a cunning move by Trump, since he can claim that it was previously accepted by the Obama administration. The 2015 Act was a bipartisan measure that aroused very little opposition in Congress, though it was criticised at the time by several rights organisations, including the American Civil Liberties Union which described it as "blanket discrimination based on nationality and national origin without a rational basis".

Trump's review of visa procedures, as set out in his executive order, will "determine the information needed from any country to adjudicate any visa, admission, or other benefit ... in order to determine that the individual seeking the benefit is who the individual claims to be and is not a security or public-safety threat". It will also compile a list of countries that "do not provide adequate information" for this purpose.

Countries that are deemed not to provide the US with adequate information about their nationals will be given 60 days to comply. Citizens defaulting countries will then be barred entry to the US under a new "presidential proclamation".

The implication of this is that although the seven-country ban has been presented as temporary, Trump intends to place a permanent ban on citizens from countries yet to be identified, and the list may be larger than the current seven.

While it might not be unreasonable to expect governments to share information about their citizens for security purposes, the effect of Trump's plan would be to penalise ordinary people for the failings of their governments.

It's also worth pointing out that the countries least likely to cooperate in providing information are those with failed or failing states (such as Yemen and Somalia), or those where the government is hostile towards the US – in other words, the countries that are most likely to be the source of refugees or seekers of political asylum. 

Trump has already vowed to drastically reduce the number of refugees entering the United States, and this may be one way of doing it.