Following the fall of the Taliban government in Afghanistan, the country debated a new constitution. Reports from outside advisers were commissioned. Political talks were held in Germany and, in the end, a new constitution was agreed in early 2004.
The 2004 constitution established a presidential system. However, for quite a while it appeared as if Afghanistan would adopt a semi-presidential system.
The best way to track the constitutional debate is to go to the website of Barnett R. Rubin, who was one of the advisers on the constitution. This website provides copies of the various briefing papers. It is a really nice resource for what governments are told about the pros and cons of different regimes, including semi-presidentialism.
In addition, Dr Rubin has an article on the process in Journal of Democracy, vol. 15, no. 3, July 2004. On pp. 11-12 there is a good resume of the debate. He makes it clear that the political class, or considerable parts of it, were willing to adopt what was, in effect, a semi-presidential system. However, there was opposing advice and, in the end, a different system was adopted.