You can’t contribute if you are not a US citizen
Edited to add the following:
Here is a poll that was just released: http://www.angus-reid.com/polls/index.cfm?fuseaction=viewItem&itemID=12600
If you are a US citizen you can either contribute directly through their site’s contribution page, https://www.onlinesslserver.com/pederson2006/contribute/
You can also go to http://www.pederson2006.com/ and navigate through there.
Or you can probably contribute if you call their HQ at (602) 262-2006
You might want to choose the last option if you are a US citizen but currently overseas, as they might block transactions from foreign IPs.
Also, if you are not a USA citizen, don’t contribute; the election laws are rougher than you might think for foreign nationals trying to influence US elections.