Given that we do not live in a world where libertarianism is generally favored, libertarian realpolitik asks the question: What policies should a libertarian support to make things best, from a libertarian perspective, out of a generally unfavorable political environment?
In the libertarian realpolitik world, tradeoffs can be supported between various policy issues some of which can move society in a direction away from liberty if at the same time it results in greater liberty on other issues.
Since tradeoffs can only be valued by individuals in subjective fashion, there is no "libertarian" answer to what tradeoffs should be supported. Different libertarians, based on their subjective value scales, can weigh the tradeoffs in opposite fashion.
However, in many cases, it will be obvious from empirical observation what the general consensus will be from a libertarian realpolitik perspective. For example, if we have the option of choosing between a ban on Number 2 pencils and a ban on Empire building wars, the obvious choice of most would be the ban on Number 2 pencils.
Note well: From a pure libertarian perspective, there should be no ban on Number 2 pencils and a ban on Empire building wars. Libertarian realpolitik is one step away from pure libertarianism. It asks, what can practically get done in the here and now?