I’ll answer.
First, it really depends what you mean by “the political right”. In general, the right advocates for smaller, decentralized government (e.g. lower taxes, less regulations), and upholding tradition and institutions (e.g. Constitution, religion). The left centralizes power in the name of “progress” and revolution, overthrowing tradition and institutions.
Islamism wishes to impose a top-down system of government and overthrow all existing institutions and can therefore be viewed as leftist. Authoritarianism and nationalism are not automatically on the right. Remember that Marxism itself was fascist, elitist, nationalist, and brutal, and that Nazism was the National Socialist party, with government control of all institutions and the coopting of some that were formerly private.
Second, the left does not support the Islamists because of their left or right orientation. It supports them because they are both anti-American. Witness the left joining in burning the American flag at Hamas rallies.
