...don't use the word "intelligent". Just drop it altogether. No need to change the tone or target of your letter by using words GOPers see as "negative". Use their language, but not in a way they feel threatened.
I would put emphasis on donors, so that the mention of the Bush pioneers is less on Bush and his nicknames and more on campaign financing:
In 2004, oil industry donors dominated the Republican presidential campaign.
And then, use total dollar amounts for the 13 donors without using names.
I would change the McCain sentence to read:
Now, after receiving nearly $500,000 from the oil industry, John McCain has proposed they get tax cuts, despite their record profits.
Also, I would remove the word "intelligent" and change the word "masters" to "most aggressive donors" and "our nation" to "we", so your last paragraph reads;
Do the readers of The Daily Light really believe that our elected officials are serving OUR interests…or those of their most aggressive donors? Please research your candidates, and don’t rubber stamp a vote; we can’t afford it.