Todd Moss and Stephanie Majerowicz over at the the Center for Global Development predict that starting soon, as a result of the recent election, aid to Africa will likely drop by $900 million per year beginning in 2012. They analyzed U.S. aid flows to Africa between 1961-2008 and found that aid decreases significantly when the Presidency and Congress are controlled by different parties.
This result is driven by different parties in the White House and on the Hill–not because Republicans are structurally anti-aid. Yes, the GOP has plenty of vocal foreign aid critics, but the record is pretty clear. In fact, ODA flows to Africa are highest under all Republican control, followed by all Democratic control. The combination for the next two years–Democratic White House and Republican/split Congress–is actually the lowest configuration.
I would be interested in learning why it is that aid decreases. My guess is that when a Democrat is in the White House, the Republicans pretty much oppose any increase in spending, regardless of what it's for. Not sure what the cause would be when the situations are reversed.
As for the why aid is greater when the Republican's control Congress and the Presidency, I'm guessing that (in the past) it has to do with increased aid to non-aligned countries during the Cold War as we competed against the Soviets for influence in Africa. More recently, however, there was a dramatic increase under Bush the Younger who quadrupled aid to Africa, mainly to fight HIV/AIDS, tuberculosis and malaria.