Elected Officials may not accept campaign contributions from corporations.
How the system got to be this way and why. What were the driving forces?
It all began in 1907 with theTillman Act, Teddy Roosevelt stated in his annual address before Congress:
All contributions by corporations to any political committee or for any political purpose should be forbidden by law; directors should not be permitted to use stockholders' money for such purposes; and, moreover, a prohibition of this kind would be, as far as it went, an effective method of stopping the evils aimed at in corrupt practices acts. Not only should both the National and the several State Legislatures forbid any officer of a corporation from using the money of the corporation in or about any election, but they should also forbid such use of money in connection with any legislation save by the employment of counsel in public manner for distinctly legal services.
The Act didn't have any teeth, because it lacked penalties and an enforcement method. Congress would later pass the Federal Corrupt Practices Act
The 1910 Act established campaign spending limits for political parties in House general elections. It was the first federal law to establish public disclosure of financial spending by political parties (but not candidates) by requiring the national committees of political parties to file post-election reports regarding their contributions to individual candidates and their own individual expenditures. However, the 1910 Act only covered single-state political parties and election committees, carried few penalties and was rarely enforced.
The FCPA was repealed when the 1971 Federal Election Campaign Act was passed. It was amended several times. It established the Federal Election Commission and increased disclosure of contributions for federal campaigns. It was amended in 1974 to place legal limits on the campaign contributions.
Corporations are currently prohibited from making campaign contributions.
Corporations, Labor Organizations and National Banks
Contributions made from the treasuries of corporations, labor organizations and national banks are prohibited. Additionally, national banks and federally chartered corporations may not make contributions in connection with any election, including state and local elections. Contributions may, however, be made from separate segregated funds (also called political action committees or PACs) established by corporations, labor organizations, national banks, and incorporated membership organizations. 11 CFR 114.2 and 114.5.
Political Action Committees have First Amendment rights (see Citizens United v. Federal Election Commission
If the First Amendment has any force, it prohibits Congress from fining or jailing citizens, or associations of citizens, for simply engaging in political speech."
As for how this is different than bribery, it would require that the campaign contribution was given to the government official with the promise to influence an official act; aid in committing fraud; or for them to omit doing their lawful duty.