Pre-, A- and Post-Millennial
For Leithart, since the two beasts of Revelation are to be identified with Neronian Rome (sea beast) and Herodian Jerusalem (land beast), the destruction of both in the lake of fire must occur in the crisis of AD 66-70. Revelation 19, then, does not refer to a future advent of Christ, but one which happened in the first century, at the start of the church age. As such, the coming of Jesus is
... simultaneously pre-, a- and postmillennial. It is premillennial because Jesus comes prior to the beginning of the millennium; it is amillennial in that it does not take the 1000 years literally, and does not distinguish the 1000 years from the current age of the church; it is postmillennial because, in the sequence of Revelation, the final judgment and the consummation of the marriage feast take place after the millennium is completed.
Of course, there is no way of affirming all of the claims of all three systems, and Leithart does not intend to. At a systematic level, he is pretty much where Augustine was, and is little different from classic amillennialism. But his reading has the merit of incorporating several of the exegetical strengths of the premillennialist view, without collapsing into a radical preterism that avoids a future return of Christ altogether. Whether you find it convincing or not—and to make the case fully takes much longer than this—it is a fascinating synthesis.