So it seems that due to imprecise language people disagree on the exact place of the red line the US (and Israel) were drawing. The post you responded to was indicating that the red line was, as a sibling comment mentioned, the breakout time from political decision to working nuclear weapon. Many other people, yourself included, seem to consider the red line to be the political decision itself. This red line now may be crossed in response to our first strike after their violation of the breakout time red line. If we were successful it seems as though the message is clear, we will use overwhelming military force to prevent them from having a nuclear weapon. So even if the political decision gets made to build one, any attempt to restart the process - which isn't exactly stealthy - will be met with similar force. If we failed though, then we might get to see a nuclear weapon being used in modern times.