The Republicans came into power promising to push a tax break from the beginning of the campaign. It was a crucial part of the 2016 campaign and their promise to voters.

They aren’t going to sue AT&T over a non-legally binding statement in a speech nor would they have legal standing to do so even if they wanted.

If there was, that organization would announce an investigation that was quickly concluded with a redacted report and confidential hearing and no further action. The chairman of said agency would then mysteriously get a high-paid position as an advisor to the AT&T board of directors, a job that necessitates a young female intern and frequently requires travel to countries with legal prostitution.

Why would the government currently being run by people who are perfectly happy with this want to sue?

It brings up an interesting point. The supposed motivation of the tax cuts was under the guise that it would increase jobs and mean more money for employees. I have a hard time believing anyone who voted for the tax cut actually believed that. And the people lobbying for the tax cuts are not legally obligated to make good on any of the things they said would happen when the tax cuts went through.

The most likely thing is the people who were elected and passed the tax cuts are held accountable and then the cuts are rolled back but don't hold your breath.