Iran has responded to Trump's withdrawal from the 2015 nuclear deal by resuming the stockpiling of low enriched uranium, removing the cap on the level of uranium enrichment and resuming work at the Arak nuclear reactor, while making it very clear that those steps would be immediately reversed if the United States agreed to full compliance.
The major fact about Iranian nuclear policy before the Joint Comprehensive Plan of Action (JCPOA) was negotiated should shape public understanding of the current conflict: For more than three years, from 2012 to 2015, Iran could have enriched enough uranium at 20% enrichment level for one or more nuclear weapons, but it chose not to do so. Instead, it used the US's knowledge of that capability as leverage against the US in negotiating what eventually became the JCPOA.
The real nuclear crisis facing the United States is not that of an Iranian regime threatening a nuclear conflict. Rather, it's a US government policy that rejects the 2015 compromise and seeks to provoke Iran even further.