It's been a while. Wikipedia [1] is relatively useful here:

1890 - Start of conventional anti-trust enforcement

1930 - Ramp up of law's usage (under FDR)

1966 - First dissent against anti-trust (Brown Shoe Co. v. United States)

1974 - First decision against anti-trust (United States v. General Dynamics Corp.)

1982 - United States v. AT&T allows break up of Ma Bell. Weakened enforcement allows re-merger.

1999 - Microsoft successfully fights off anti-trust enforcement prevent company from ever being split.

If you want anti-trust enforcement, do not elect Reagan and his descendants.

[1]: https://en.wikipedia.org/wiki/United_States_antitrust_law