there's no legal impediments for the president to for congress... its up to the pampangeņos to decide on that...
as for cha-cha.. that will depend on how many congress who support cha-cha or member of the LAKaS party who will this election... and also other party members that actually loyal to LAKAS like(daghan sila nikalit lang mabak sa LP..)
if the president did win in congress and only few LAKAS members, or other party member who actually have their loyalty to LAKAS win in congress there is no room that the president will bag the coveted speaker of the house position...
so in the end the cha-cha thing and the president becoming a prime minister does not depend on who win as president but more on who will in congress...
so choose your congressman... if she/he have shown tendency to support cha-cha and a GMA supporter you might as well not vote for him/her.. because your fear just might come true...