Final answer:
The key difference between a president and a prime minister in legislative support is that a president operates independently from the legislature, while a prime minister, typically being part of the majority party in the legislature, usually commands party support for passing legislation.
Step-by-step explanation:
A major difference between a president and a prime minister regarding support from the legislative branch is rooted in the relationship between the executive and legislative branches. In a presidential system, there is a clear separation of powers with the president and legislature being independently elected and operating separately. The president sets the policy agenda but cannot guarantee the passage of legislation, as the legislature is outside the president's control. In contrast, in a parliamentary system, the prime minister is a member of the legislature and usually the leader of the majority party. This close relationship between the executive and legislative branches means that the prime minister can generally rely on the support of their party to pass legislation. As such, if the prime minister's party commands a majority in the legislature, the passage of the prime minister's policy agenda is more assured, highlighting a unified government.