Julius Caesar played a role in the decline of the republic in that he caused a great rift between political leaders, but played a role in the rise in that he greatly inspired the people.
Answer: I'm almost 100% sure that the 2nd one is correct, but I would wait for another opinion as well.
Explanation:
The democrats and republicans have influenced our current political system by sharing most of the same values and views with the American people. As their party members and those who associate themselves tend to lead more toward what the party wants.