My understanding of politics in the US is that a large portion of campaign funds come from different lobbying groups and special interests. Does this create a conflict of interest for politicians beholden to their campaign contributors in addition to their constituents? What are the pros and cons of this system as compared to an alternative system where candidates are limited to using public resources adequate to run their campaign?
Among other pros of raising private donations:
Overall, political advertising costs money (a LOT) since it not only has to compete with other political advertising but with all the NON-political ads out there. This inflates the prices of advertising to the point that no publicaly funded candidate can afford to advertise. Which in turn gives an incumbent a 100% guarantee of re-election, which is obviously bad for democracy. With no incumbent, the edge goes to a celebrity, or someone beloved by the media.
In other words, "adequate to run their campaign" is not something we have enough public money to spend on, for any definition of "adequate".
A candidate that is opposed by the 4th branch of government (media) has ZERO chance of getting their voice out without raising a substantial amount of money. Leaving aside the sure-to-generate-debate issue of whether MSM in America is liberal (but if you care, look who major newspapers editorial opinions endorsed recently), the proof is in the pudding: Media-organized debates have uniformly excluded less "major" candidates of all political persuasions.
As far as the cons, "beholden to their campaign contributors" is a nice phrase to use around the coctail table, but there needs to be some research to show that it is actually true.
FiveThirtyEight ran a post last year that raising spending on ads in a non-edge case (e.g. when both candidates are already somewhat known) by 100% merely adds 1% margin to the vote. And for any campaign other than national Prez election, advertising is the biggest expenditure (for Prez, get out the vote operations and organizing take money too).