Actually we do. Or did. The sanctions that were in place were wrecking their economy, most of which is owned by the mullahs personally. That's why Iran agreed to negotiate in the first place. But Obama lifted them as a reward for just sitting down with us, and threw away all leverage in the actual negotiations. Trump says he would walk out and double or triple the original sanctions until they begged us to negotiate.
They were proceeding with the sanctions on, putting them back isn’t really a threat. You can’t actually double or triple sanctions, once you’re not trading with somebody you’re not trading with somebody, you can’t extra not trade with them.