As far back as the early 19th century, an American President wrote about the potential dangers Islam posed to mankind: (link via Betsy's Page)
John Quincy Adams possessed a remarkably clear, uncompromised understanding of the permanent Islamic institutions of jihad war and dhimmitude. Regarding jihad, Adams states in his essay series,
“…he [Muhammad] declared undistinguishing and exterminating war, as a part of his religion, against all the rest of mankind…The precept of the Koran is, perpetual war against all who deny, that Mahomet is the prophet of God.”
It appears that over time, people tended to forget this essential truth about Islam. Here are several more recent pieces of evidence about this: Outlawing Blasphemy and Ayatollapalooza (both from The Corner) and more on the "moderate" Muslims in Texas celebrating Ayatollah Khomeni, the "Great Islamic Visionary."