While there are some nice APIs for campaign finance at the federal level, they differ significantly.
Have there been any attempts to define a data standard for campaign finance?
Political Disclosure Standard Electronic Reporting Format (PDSERF) is one such example. It may very well constitute the first such format.
Note: I'm the author of the question, answer, project parser.
In the United States, the Digital Accountability and Transparency Act (DATA) Act puts in place a requirement for U.S. federal spending to be in "open, standardized data, and to publish that data online." This will affects awards, appropriations, accounts, and payments. It may or may not have a secondary affect of bringing other financial reporting into this new XBRL standard.
Some of the key datasets related to campaign finance and transparency have been collected and made interactive at Ethics.Data.gov.
Some states, such as California, have a standard format for campaign finance and lobbying data.
Currently, there are no standards in place for campaign finance filings across the U.S. These are managed by the Federal Election Commission, which notes that each Committee has different requirements.
(Note: As of May 25, 2014, his has been passed by the House and Senate, and awaits the President's signature before it is law.)
