Depending on what policy a politician wants to push he can cite either traditional economics or Keynesian economics
I'm kinda curious what exactly you mean by "traditional economics".
Before Keynes, economics was dominated by the Austrian School, which didn't believe in testability and relied mostly on deductive reasoning based on fixed axioms. In other words, it wasn't really a science, but a branch of philosophy. This is probably the best candidate for a "traditional economics", but the problem here is that since it eschews tests, a clever person can argue any position they like with it by carefully crafting their axioms and reasoning.
Some people today really love that property, so they still use it. Particularly the really wealthy (the Koch's have actually endowed some Austrian-only economics schools). However, this is far out of the mainstream, and would probably not even exist today if not for that patronage.
Keynes turned economics into a science (a "dismal" one, but a science nonetheless). So if we discount the economic philosophers, Keynsian economics really *is* "traditional economics". Other schools are newer, and generally arose to address perceived limitations in Keynsian economics. The Keynsians meanwhile have been expanding their model to cover useful innovations in the other schools.
So basically there are two points here:
- Keynsian econ *is* traditional economics
- A lot of so called "economists" promoted on TV are actually Austrian economic philosophers. Watch out for them. If someone feels they can't use science to promote their view, that should tell you something right there.