1
general::
Become stuck, be unable to progress, as in Their research bogged down because they lacked the laboratory expertise. This expression transfers sinking into the mud of a swamp to being hampered or halted. [First half of 1900s]
American Heritage Idioms
2
general::
Phrase(s): bog down
to become encumbered and slow. (As if one were walking through a bog and getting stuck in the mud. Often preceded by a form of get.) • The process bogged down and almost stopped. • The truck got bogged down in the mud soon after it started.
McGrawhill's American Idioms And Phrasal Verbs