Complex sentence: The appointment was intended dramatically to reinforce the point that the PDPA was going to take a back seat; in fact, the new constitution vests key powers in the presidency, and there was no indication that Najibullah was prepared to give up that central role.
Split into simpler sentences: The appointment was intended dramatically to reinforce the point that the PDPA was going to take a back seat. However, the new constitution vested key powers in the Presidency, and President Najibullah did not give up that central role.