Retired professor of math and computer science having taught for 36 years at a state supported university in Virginia. United States Senators serve a term of six years in office. There is no limit on how many terms a Senator can be elected to serve.
Herbaceous perennials are garden plants that die back to the soil line when winter temperatures arrive. The plants enter a dormant period and strengthen the root system while waiting for the coming of spring.
In the simplest terms, a perennial is a plant that lives for at least 3 or more years. We usually use this term to describe herbaceous perennials when talking about gardens.