While I strongly support DC statehood, I don't understand why Democrats are pushing for DC to become a state and not Puerto Rico.
As compelling as the case is to make DC a state, PR's case is even strong. DC currently gets one electoral vote, far less than it would as a state, but that single electoral vote is still more than PR gets. PR literally has no voice in the Presidential election even though it is part of the U.S. While DC statehood proponents note the fact that DC's current state leaves almost 700,000 U.S. citizens without full representation, PR has over three million U.S. citizens with even less representation.
But most importantly, in the last election Puerto Rico held a referendum about the future of the island, and statehood got a clear majority. While opinion polls show that DC enjoys about the same percentage of approval in DC among DC residents as the "yes" votes in the PR referendum, polls are not as reliable as an actual election.
The DC effort has a potential constitutional issue in that the Twenty-Third Amendment contemplates that DC will be a federal district and not a state. While the current DC statehood bill sets aside an exclusively federal district within the new state of DC to satisfy those constitutional concerns, I have no doubt that any DC statehood would immediately be subject to a constitutional challenge and our current hyper-partisan results-oriented 6-3 conservative majority on the Supreme Court would have an easy basis to declare the whole effort unconstitutional. PR raises no constitutional concerns and any legal challenge would likely go nowhere.
Ideally, Democrats should push for statehood in both DC and PR (and other territories as well if they think it can work). But if there is limited political capital to spend on a statehood bill, Democrats should throw their weight behind PR statehood, not DC. Because even if they win passage of a DC bill there is a fair chance the Court will strike it down. If a bill to make Puerto Rico is passed, Puerto Rico would become a state, it is as simple as that. No court challenge would be likely to stop it.