I will be involved in Capitol manoeuvring almost entirely? Not if this (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

I will be involved in Capitol manoeuvring almost entirely? Not if this [I in *(CAPITOL)] + AL <l> (=entirely; “almost” means last letter is dropped); “manoeuvring” is anagram indicator; semi- & lit.