Body politic
A group of people organised under a single government or authority (national or regional) is a body politic.
Carpetbagger
A carpetbagger is an opportunist without any scruples or ethics, or a politican who wants to represent a place they have no connection with.
Economical with the truth
(UK) If someone, especially a politician, is economical with the truth, they leave out information in order to create a false picture of a situation, without actually lying.
Fifth columnist
(UK) A fifth columnist is a member of a subversive organisation who tries to help an enemy invade.
Fourth estate
This is an idiomatic way of describing the media, especially the newspapers.
Get on your soapbox
If someone on their soapbox, they hold forth (talk a lot) about a subject they feel strongly about.
Gunboat diplomacy
If a nation conducts its diplomatic relations by threatening military action to get what it wants, it is using gunboat diplomacy.
Megaphone diplomacy
If negotiations between countries or parties are held through press releases and announcements, this is megaphone diplomacy, aiming to force the other party into adopting a desired position.
On the stump
When politicians are campaigning for support and votes, they are on the stump.
Pork barrel
Pork barrel politics involves investing money in an area to get political support rather than using the money for the common good.
Toe the line
If someone toes the line, they follow and respect the rules and regulations.