They've contributed to political candidates an dpolitical parties. There are other examples but those are two recent glaring ones. Soft money is important in a campaign because it's easy to raise. There are no limits. Rather than contacting thousands of people to raise a small amount of money, one person can give a million dollars if they want to.
Corporations are unable to make political contributions.
It's been illegal for a corporation to make a political contribution since the early 1900's. Yet, corporations can contribute unlimited amounts of soft money to the political parties. It has been illegal for labor unions to take labor union dues and spend them on political contributions since 1947. However, labor unions can contribute millions of dollars in soft money. It's easy to raise soft money and because both political parties are pushing the law to the limit, 30-second soft money ads are influencing elections all across America.