The line of succession was:
Speaker of the House
Senate Pro Tem
then, Al Haig—so it looked like he was planning to bump off the VP, Speaker and Pro Tem in one decisive maneuver. ;-)
He was saying “at that time” he was highest ranking person present in the Administration.
I watched it live. My impression he was just trying to calm people that there was no chaos at the White House. I didn’t think for a second he was talking about succession. But, hey... the MSM narrative lives on.
In his book he states he was running the White House staff, not the government, and AF that time all the toadies in line were out of touch.