As citizens and voters, atheists of every nation have a vested interest in the direction which their country takes. Atheism may not entail any necessary positions which all atheists must, as a matter of course, support, but there are positions and values which atheists should support because they are necessary for a secular, liberal democracy to function. There is no "atheist voting block" as such, but atheists - as individuals or while working in groups - may be able to influence society and government through the application of reason, skepticism, critical thinking, realism, and humanistic values.
Should Atheists Vote their Atheism?Some have argued that atheists should "vote their atheism," but what could that possibly mean? Atheism isn't a philosophy of any sort, much less a political or social philosophy which could inform how one votes. At best, it might mean that a person shouldn't vote for someone they know is an anti-atheist bigot and who will work against equality for atheists - but doesn't that go without saying? There are many things which atheists should vote to defend, but none are necessary and automatic consequences of their atheism. You can't "vote your atheism," but you should vote your humanistic values.
Some have also argued that atheists shouldn't vote at all if there are no candidates who make an attempt to appeal to atheists. This makes less sense than voting one's atheism: atheists are such a diverse group that it's hard to see what a candidate would do to appeal to atheists generally. The most a candidate could do is acknowledge that atheists are not inferior and deserve to be treated as equals. While it makes no sense to vote for someone who does this yet supports no humanistic values, it also makes no sense to vote for someone who doesn't regard atheists as equals. You shouldn't vote for anti-atheist bigots who deny your equal rights or dignity.
Voting to Defend the Establishment Clause of the First AmendmentOne thing which atheists should take into consideration when voting is which candidate will do the most to defend the First Amendment - not just the Free Exercise Clause, but also the Establishment Clause. All candidates at least pay lip service to the importance of religious freedom, but few express clear support for the idea that government has no authority to promote, endorse, encourage, or support any religions, religious institutions, or religious beliefs. Most candidates are religious theists who to look favorably on government support of some sort for religion.
Voting to Defend SecularismA related issue which atheists should take into consideration is secularism, a critical component of liberal democracy which is often attacked by the Christian Right. Secularism is the political principle or philosophy that there must exist a sphere of knowledge, values, institutions, and action that is independent of religious authority. If there is no secular sphere, then everything is under ecclesiastical control and this undermines the possibility for liberty and autonomy. It's rare to find candidates who mention secularism and secularists in a positive way, so look for them and support them if you can.
Voting to Defend Science and EvolutionScience shouldn't be such an important issue in elections. Given how critical it is for modern society, every candidate should support science education and scientific research. Unfortunately, science is also a pillar of modern secularism and the Enlightenment, thus making it a target for the Christian Right. Atheists should vote for those candidates which are most likely to defend science both in the abstract and in practice: they should not shy away from accepting with the conclusions of science and they should refuse to water down science teaching to please religious superstitions.
Voting to Defend the Rule of LawPerhaps nothing is as fundamental as the rule of law: liberal democracy cannot exist unless everyone, from the lowest citizen to the highest official, is equally subject to the same laws. Unfortunately, there are always movements seeking to exempting some group from neutral, generally applicable laws and place them outside the political process. Atheists should make a point of supporting candidates who support the rule of law. Candidates who support exempting particular people (like the president) or particular groups (like religious believers) from the law should not get your vote.
Voting to Defend Personal Liberty & AutonomyDemocracy, which is "government by the people," cannot exist unless people are free and have the freedom to govern themselves. If sovereign power rests with the people, it can only be because the people are free to be sovereign over themselves and to explore the options available for structuring their government. This should be an important political principle for atheists because of the extent to which religious leaders seek to subject people to the control of religious traditions, institutions, and priests. Personal autonomy should be a prerequisite for the liberty to be an atheist in the first place.
Voting to Defend Openness & HonestyGiven how many theists have become atheists based on closer study of what religions have done, atheists should strongly support the free flow of information as a general principle. Because a working democracy requires that people be informed about what their government is doing in their name, atheists in a democracy should support candidates who promise to reduce the ability of the government to keep secrets from the people. The more power government has to keep information from the people, the easier it is for that government to abuse all of the power it has. Who would know?
Voting to Defend Equality & JusticeEquality and justice are two connected political values which atheists have frequently been denied. Without equality, only the privileged portion of the population ends up being truly sovereign; too often that's just what religious believers do for themselves - Christians, Muslims, Jews, and more. Without justice, there can be no application of the law; too often, religious believers seek to apply "justice" in religious rather than secular, neutral terms. Atheists should vote for candidates who will defend real equality and justice for everyone.
Vote with an Eye on the Future and the "Big Picture"It's tempting to look primarily at a candidate's stance on certain policy questions, but there are many more things which should be taken into account. For example, will they or their opponent do a better job when it comes to maintaining the independence of their branch of government or in using their power to ensure oversight over the other branches? Voting for the party rather than the candidate sounds bad in some ways, but which party controls the legislature matters a lot when it comes to what legislation is voted on, investigations, and confirming appointees to various courts and agencies. A candidate's policy positions are important, but the long-term effects of their holding an office must be considered.