Raising the bar once again for US political controversy, Donald Trump called on Monday for "a total and complete shutdown of Muslims entering the United States".
The Republican presidential frontrunner claimed that research by the respected Pew organisation showed a "great hatred towards Americans by large segments of the Muslim population" - but he did not refer to any specific study to support that claim, and we can't find one that does.
Mr Trump did cite a specific a study by the Center for Security Policy - "very highly respected people, who I know, actually" - which he said showed that 25% of Muslims in the US believed violence against America was justified "as part of the global jihad".
Mr Trump's press release:
But what exactly is the Center for Security Policy, and just how highly respected is it?
It's a conservative think-tank
The CSP was founded in 1988 by Frank Gaffney Jr, a former staffer in the Ronald Reagan administration who has been accused of Islamophobia. On its website, the centre calls itself a "Special Forces in the War of Ideas" which offers "maximum bang for the buck" to its donors.
The CSP does not publish information about who those donors are, but according to a 2013 report by Salon they include some of the US's biggest aviation and defence companies - Boeing, General Dynamics, Lockheed Martin, Northrop Grumman, Raytheon and General Electric.
Promoted on the organisation's website are reports and books with titles such as Star Spangled Sharia, Civilisation Jihad, and Muslim Colonisation of America. Responding to the controversy over Mr Trump's remarks, the CSP said it was "necessary to respond to the threat posed by jihadist terror in a way that ... calls it what it is".
It's not very highly respected
The CSP has been criticised across the political spectrum - by high-profile Republicans as well as Democrats - and by organisations which monitor extremist groups. Terri Johnson, executive director of the Center for New Community and J Richard Cohen, president of the Southern Poverty Law Center, called it "an extremist think-tank" led by an "anti-Muslim conspiracist".
The group was heavily criticised in 2012 after it repeatedly accused Huma Abedin, an aide to Hillary Clinton, of being a secret member of the Muslim Brotherhood. Leading Republicans including John McCain and John Boehner denounced the accusations.
The CSP has been criticised by a wide range of extremism monitoring organisations, including the Anti-Defamation League, and Center for Democratic Values at City University of New York.
Does its research stand up?
Arguably, no. According to the Bridge Initiative, a Georgetown University Islamophobia research project, the CSP survey was an online, self-selecting poll of 600 people, meaning respondents opted in to taking part.
Self-selecting internet surveys are less reliable that more traditional, random polling methods, because the opt-in element can lead to bias. Then there are the existing views of the organisation commissioning the poll - the CSP - which may have influenced the outcome.
The Washington Post called the poll "shoddy". According to the Post, the question had an agree/disagree answer format with agree in each case linked to the more controversial option - favouring Sharia law or supporting violence. Researchers say this format is affected by "acquiescence response bias" - we are generally more likely to favour agree options.
The CSP said in a statement on Sunday that its research methods were "consistent with international industry standards".
Who is Frank Gaffney Jr?
Mr Gaffney Jr served in the Reagan administration during the 1980s but left in 1988 to form the CSP, after his nomination as assistant secretary of defence was rejected by the Senate.
"Once a respectable Washington insider," according to the Southern Poverty Law Centre, which monitors US hate groups and extremists, Mr Gaffney Jr became "one of America's most notorious Islamophobes", the SPLC said.
Mr Gaffney Jr has repeatedly accused parts of America's Muslim population of what he calls "civilisational jihad". He has also called for Muslims to be investigated by a "new and improved" House Un-American Activities Committee - a highly controversial Cold War-era body which questioned and blacklisted US citizens accused of being communists.