So lets take a look at the body of evidence here.
If the Iranians are reportedly willing to conduct an attack in the United States, are they planning one?
Clapper's testimony is that U.S. officials have seen no intelligence to indicate that Iran is actively plotting attacks on U.S. soil.
Then why would the Director of National Intelligence say Iran may be plotting an attack?
Because of what the Iranians have already plotted - last year's plot to assassinate the Saudi Ambassador.