The deal negotiated with Iran includes many measures to block its progress towards making nuclear fuel, mostly lasting 15 years.

I think this is sufficient. In 15 years, the situation is likely to change so much that there is no point worrying now about what to do then. The US and Iran might be allies.

Republicans hate this deal, because they want a war instead.

Of course, the religious oppression in Iran is still outrageous, and oppression of dissent too; but not as bad as in Saudi Arabia and Egypt, which the US considers allies. We should try to end those forms of repression, but we have little influence over Iran. One thing we know is that economic warfare doesn't help.

Without this deal, nothing could stop Iran from developing nuclear weapons if it tried to. I think that Iran did in the past intend to develop nuclear weapons, but the weakness and division of Iraq removed the main military threat to Iran, so now Iran would rather forego nukes and get the sanctions lifted.