Standard federal candidate political donations are limited to $2700 per candidate per election. The primary and general elections are different elections for this purpose.
There are no tax implications to a campaign contribution. Even if you contribute to the campaign of someone to whom you have made gifts now or in the past, that does count. You are contributing to the campaign, not the person. Such money has to be used for campaign purposes. The candidate could be prosecuted (for something like embezzlement) for using the funds for something else.
Example source: http://www.rothcpa.com/archives/006985.php
Congress itself ordered the IRS away from direct political contributions by enacting what is now Code Section 2501(c)(4) in 1975, which prohibits gift tax assessments on "political organizations," defined by Section 527 as "...a party, committee, association, fund, or other organization (whether or not incorporated) organized and operated primarily for the purpose of directly or indirectly accepting contributions or making expenditures, or both, for an exempt function."
There is no way to donate to a candidate's campaign in a tax deductible way. The only tax-deductible money in politics is money given to a charity that the charity then uses to fund their own campaigning activities like advertisements or get out the vote calls. Such spending might supplant some candidate spending, but it can't be given to the candidate's campaign to spend. In fact, such spending can't be coordinated with the campaign at all.
Example source: http://blogs.hrblock.com/2013/03/04/how-to-capture-political-contributions-on-your-tax-return/
If you wrote a check for a presidential candidate or even a local mayoral candidate, you’re out of luck when it comes to deductions. Contributions given directly to campaigns and parties are absolutely non-deductible.
Note that it spends a lot of time explaining how you can deduct contributions to independent charities that happen to do campaign work.