Does the constitution ensure that the president and congress will fight for power?

No. it isn't

Explanation:

Constitution only ensured that proper checks and balances exist between the president and congress so they do not become too powerful. The president was granted with the power to veto the Congress and passed its own laws, and the congress was granted with the power to vote and override the veto.

They don't have to always fighting for power, there are times when President and the Congress have to work together for the good of the nations. But the constitutions definitely ensured that they can limit each other.