Lyndon Johnson successor (5)
I believe the answer is:
nixon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lyndon johnson successor</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for nixon that I've seen before include "US president, d.1994" , "Watergate US president" , "US president before Gerald Ford" , "President re-elected in 1972" , "Only US president to have resigned from office" .)