What does "foil" mean in this context?
"Cruz bubbled up from a weak field of rivals, and Tuesday confirmed his emerging reputation as an impressively poor foil to Trump."

Please, also this word: "tar"

" Republicans blamed the candidate Todd Akin, who used the phrase “legitimate rape” during the Missouri Senate race, for tarring the Party with the image of a waging a “war on women.” "

http://www.newyorker.com/news/news-desk/trump-versus-clintons-woman-card In 2012,

Thanks in advance.

Question

What does "foil" mean in this context?
"Cruz bubbled up from a weak field of rivals, and Tuesday confirmed his emerging reputation as an impressively poor foil to Trump."

Please, also this word: "tar"

" Republicans blamed the candidate Todd Akin, who used the phrase “legitimate rape” during the Missouri Senate race, for tarring the Party with the image of a waging a “war on women.” "

http://www.newyorker.com/news/news-desk/trump-versus-clintons-woman-card In 2012,

Thanks in advance.

Answer

"A foil to" someone (or something) in this case means the opposite of someone or something.

To "tar" means to tarnish/taint the image of someone to the point of humiliation. It originates from "tar and feathering" where people would be punished by being covered with tar and having feathers put on them. It was punishment meant to humiliate.