Shelia took the rap for her brother when he broke the antique lamp. what figurative language is this and how do you know?

It is an Idiomatic expression.

Explanation:

An idiomatic expression is a phrase or group of words whose meaning cannot be deduced from the literal words used. In the sentence above, 'to take the rap', simply means to take the blame for an offense for which the individual may or may not be guilty of. So, Sheila was blamed or punished when her brother broke the antique lamp. The native speakers of a language are quite familiar with the idiomatic expressions in their language.  

I knew that the phrase, 'took the rap', was an idiomatic expression because I could not easily deduce its meaning from just the literal words used. So I understood that there must have been a deeper meaning to it.

from the political point of view it could be said that the candidate   is an effective speaker because she takes a strong position on the issue. it is an open discussion but probably she is making a presentation and can choose which subjects she wants to address. she is very likely to attain her aim which is to convince voters to accept her proposal.