"incumbent' is the word you want. I think.
an open seat
a person who is running for office is a candidate
The people in a Representative's district are called constituents.
Proportional representative or a parlimentary system.
Just like in the United States federal government, state congress consists of Representatives and Senators. Sometimes to avoid confusion, it is clarified by saying "state senator" or "state representative.
A senator is a senator-elect until he is sworn in (normally in January following an election). A senator newly elected is called a freshman senator.
The senator for the Abuja FCT is called Sidi Ali.
The senator for the Adamawa south is called Folashade Bent.
The senator for the Adamawa Central is called Jibril Mohhamad.
The senator for the Adamawa North is called Mohammed Mana.
A Senator...
State representatives are charged with representing their constituents. They are responsible for proposing laws and voting on laws that are presented in the House.