1. Corporate spending in politics has had negligible impact after Citizens United: https://www.nber.org/papers/w30352
2. These days, the ostensibly pro-business party(GOP) gets more of its money from individuals and SME donors than the Democratic party.
Your real problem is public opinion itself. The public in America simply trusts corporations over government institutions(except maybe the military). David Shor has great(but damning for progressives) analyses of this phenomenon.
EDIT: I'm a recentish immigrant, so help me out with this inconsistency: Why Democrats and not Democratics? Why Republicans and not Republics?
"Republican" and "Democratic" are modifying the noun "Party" when referring to the political organizations, so you use the adjective in those cases.
Republicans are members of the Republican party
Democrats are members of the Democrat party
I’ve run a US Senate campaign. We raised tens of millions of dollars, and I can confidently say that corporate donations made no impact in any policy decisions - on the campaign or the official side.
That extends to individual donations as well. The caps are ~$10,000 per couple. Considering the cost of a federal campaign, no person or corporation can buy a campaign when costs are in the tens of millions and contribution caps are in the thousands.
It's also probably worth drawing distinctions around the different meanings of "corporate." The sense of "large for-profit, limited liability business entity" has eclipsed all other meanings, which is a shame.
Isn't that overstating the case?
I agree corporate lobbyists have an outsized and often harmful impact. But just recently we have seen California moving toward ending sales of gasoline-powered cars. Or at the federal level, greenhouse gasses are now legally a pollutant that the EPA can regulate. With just one more Democratic senator, we would have seen the end of the carried-interest loophole. And organized labor, which serves as an important check on corporate power, has been on the rise, in part due to Federal support.
I'll also note that places like Facebook, although not yet particularly regulated, are running scared from a lot of proposed legislation, and so are increasing transparency and reducing harm in hopes of heading it off. That too checks corporate power, and is a strong sign that they don't see themselves as untouchable.
Personally, although the challenges are large, I think there's a fair bit of cause for optimism.
We actually live beyond a time where this is possible. The political conditions of the US have basically deteriorated to where any meaningful regulation of corporations can't really happen because of the changing laws around how corporate contributions to political campaigns work. It actively hurts whichever political party attempts to regulate (by reducing finical contributions/increasing them to the other party or rivals in primaries who "stay in their lane".)
The only group who benefits from regulation are individuals who live in the country, which really isn't enough to get laws passed.