Partisanship creates division among political parties and it is very difficult to come into terms or get an agreement on any proposal because neither side wants to lose.
With this scenario, the President needs to mobilize the members of his party to make things work in Congress. A polarized political situation makes it difficult for the President to pass hiss initiatives in Congress, and congressmen find difficult to pass theirs too for the Presidency's faculty to exercise his veto. Then, the country is in some king of paralysis. None of them have a "free pass" to approve nothing.
In this case, the President travels to the places where their party won the election to ask for the support of partisan voters instead of common citizens.
Partisanship can severely limit the congressional power of the president. As part of the executive branch, the president has the ability to veto any law passed by Congress. This means that he can stop it from becoming a law.
However, Congress can override this veto by a 2/3rds vote in both the Senate and House of Representatives. In this case, if there is partisanship in one political party that has a significant majority in each branch of Congress, they can override his vetoes and continue to pass laws without his/her approval.
