Final answer:
The provided statement is a simple sentence, with just one independent clause regarding the U.S. Senate's uncertainty due to the Georgia runoff.
Step-by-step explanation:
The statement "Awaiting Georgia runoff, U.S. Senate and its committees have been plunged into uncertainty" is a simple sentence. Although it may seem complex due to its length and the ideas it encompasses, the sentence has only one independent clause and no dependent clauses, making it a simple sentence in terms of grammatical construction. It presents a single main idea about the status of the U.S. Senate and its committees due to an impending event, which is the Georgia runoff.