Why can Structural theory help with Viewing the President and PM actions?

-Structural Theory helps to examine the Extent of Power. A President threatening to Veto Legislation, if it knew Congress would Override it would be Priceless. Many of the President's Decisions must be Weighed against the Likelihood of the C+B System being Effective. In the UK, the PM has Powerful Whips allowing the PM to Dominate Parliament. With Fused Powers, the PM can do whatever it needs with little Compromise