In his 2015 speech, Obama said that without an agreement limiting Iran's nuclear program in return for sanctions relief, any U.S. administration would be left with only one option to prevent Iran from getting a nuclear weapon — "another war in the Middle East."
Obama said that Iran — unrestrained by the nuclear accord — would soon be on the threshold of developing an atomic bomb. "Without this deal, Iran will be in a position — however tough our rhetoric may be — to steadily advance its capabilities. Its breakout time, which is already fairly small, could shrink to near zero."
"Does anyone really doubt that the same voices now raised against this deal will be demanding that whoever is president bomb those nuclear facilities?" Obama said.
Anyone who knows anything about the situation knows that the purpose of the new sanctions is to encourage a terrorist attack or further Iran military actions against the US either of which would cause the US to attack Iran. If Iran wants to develop nuclear weapons, there is only one way to stop them, war followed by a US occupation. Trump as well as top republican leaders are well aware of this and are not particularly concerned about a 4th war in the Middle East started under leadership of a republican president. The reason is voters tend to re-elect an incumbent, and even more so during a war. It worked for Roosevelt, Nixon, and Bush.
The purpose of the Obama nuclear deal was to delay nuclear weapons development in Iran for 10 years to give the development of free enterprise and capital from the west a chance to modernize and change the country. That deal now of course is dead and gone, leaving military action as the only alternative.