Knowing the Sherman Antitrust act was to protect competition, why and how would politicians affect the competition if they invested in business?

If a politician invests into a business then there's a conflict of interests. That is because the company where they invested would give them money in return from its earnings, so the politician would want to protect the company that they invested in. If someone was their competition, a politician could use legal acts or be corrupt and eliminate competition that could harm their earnings.