If they're applying to work in a church, or any other job that involves a high standard of morality of course they should. If they're applying for a job totally void of all morality and conscience, like the president of the United States there's no need to ask. In the case of Barack Obama his past history of drug dealing, drug use, ties to terrorists, Marxists and radical reverends would have disqualified him from a bus driving position, but it was no problem whatsoever when it came to the presidency.
Employers should be allowed to ask the questions, but applicants should not be required to answer not should the employer consider the answers to those questions when making hiring decisions. So yes, they should be allowed to ASK the questions but not consider or require and answer to the question.
Americans are so diverse in beliefs and no one should be thrown out because of a political or religious standpoint. Religion is protected by the Civil Rights Act and supervised by the EEOC. Absolutely not acceptable. Political standpoint, that's really not a good thing...You should be able to work with people of differing views.
I work with so many staunch Republicans, that I've added them on Facebook and it's really diversified my news feed! It's nice. Although politically we may often (but not always) disagree, we worked well together and it didn't matter. It really depends on how mature you are as a person.
Two things that should be avoided at work: Religion and Politics. No one's right but they all think they are!
There are many other questions and scenarios that can be posed during an interview that will help judge the morality of a potential employee. Their private religious or political views should have no bearing on employment. Of course there are always exceptions. Jobs directly related to religious or political organisations and jobs indirectly related (reporters & news organizations with a specific slant, etc.). A persons private views should be just that, private. That's not to say that a company does not have the right to pass over someone for employment that is vocal and public (news, Facebook, blog, twitter, etc) about views that would cast a negative impact or do not coincide with a companies views. Or that a company could not institute a morality type clause in their employment contract stating that certain behavior or expression of public opinions against the views of the company will be grounds for termination.
To allow an employer to consider political views unrelated to the job at hand is to forfeit everything the Civil Rights Act was made to protect. Not only that, but if we allow this it could allow rich to manipulate votes by telling employees what to think. This is a step towards an oligarchy and tyranny of the rich and must not be allowed.