Answer:
Straw Man
Explanation:
A straw man is a form of fallacy whereby a speaker in debate refutes his opponent argument, but he, in fact, refutes an argument his opponent did not present at all. In this example, Senator Johnson is hitting a straw man since he does not counter Senator Smith's argument of preventing Iran of obtaining nukes. How can, as per Johnson's argument, then Iran destroy Israel if it is prevented in obtaining nuclear weapons?