Final answer:
Corporations are the group that contributes the most money to political campaigns, able to donate unlimited amounts to super PACs, as per the Supreme Court decision in Citizens United v. FEC.
Step-by-step explanation:
According to the Supreme Court decision in Citizens United v. Federal Election Commission, corporations and unions can donate unlimited amounts of money to Political Action Committees (PACs), specifically super PACs. Super PACs may not contribute directly to individual candidates but can spend unlimited sums to advocate for or against political candidates.
Hence, the group that contributes the most money to political campaigns is corporations, as they, alongside wealthy individuals, wield significant financial influence in politics through their contributions to PACs and super PACs.