If you take a rough average of the 25 opinion polls since June 2007 to test the referendum question (although the question itself has varied over time), the average in favour of a Yes vote is 49.88% - still 17 points ahead of the No vote, but nowhere near the comfortable majority that Yes campaign strategists would hope for.
Add to that all the usual ingredients of a USGA-prepared course - tight fairways, thick rough and small, quick greens - and you have the ultimate test in professional golf.