The IRS does not ask the DOJ to file suits against all delinquent taxpayers and the DOJ does not always agree to do so when asked. Usually, there is a confluence of bad behavior plus a collection statute of limitations (10-years, including additional time for suspensions) about to run. The complaint in the case is found here.
Note that the years involved are 2007 through 2011 and 2018. The years and assessment dates are schedule on pp. 4-5 of the complaint. There are some large amounts that have been outstanding for years, and certain tolling actions, i.e., the filed offer in compromise which suspended the statute. But it appears that the statute for the older years was about to run, so IRS had the choice of referring to DOJ or letting him get off the liability for the earlier years. Given his intransigence certainly hinted in the allegations in the complaint, he would not have been a sympathetic figure in the process of determining which delinquents to pursue. That is even setting aside political influence one way or the other.
This complaint appears to be a fairly standard collection suit in which the taxpayers just have been able to dodge payment.
That does not address the issue of whether politics entered the decision-making process as to whether to expend resources on a collection suit to extend the statute and enforce the then judgment lien. I can’t answer the politics question.
I will speculate that politics probably influenced the decision because if IRS/DOJ did nothing in the face of public liens for a large amount of old taxes, there would be claims that politics entered the do-nothing decision. So, from a politics perspective, IRS/DOJ were in a no-win position. But, as I said, this particular enforcement action by collection suit seems to be in the mainstream of such suits that are brought.