That's probably true, but there's very little evidence of donations to the foundation being used to elicit favors, and there's a smidge of evidence that such attempts failed. Example:
http://www.latimes.com/politics/la-na-pol-clinton-donor-chag...
http://www.latimes.com/politics/la-na-pol-clinton-donor-chag...
But there are certainly a helluva lot of ways of for this transaction to occur without anyone ever directly saying "here is your bribe".