Per
Thirteen Days, for a long stretch of the crisis the US mainland’s nuclear bombers were armed and airborne, constantly, for a potential first strike on Cuba. When the U-2 was shot down Kennedy directly threatened that another attack would result in the destruction of the defense installations and made it known as rumor he was considering nuking the island in retaliation. Curtis LeMay and some of the other cabinet staffers were sincerely in favor of a first strike throughout the conflict.
So I think we’re still quite a ways off from that level of threat.