And then there were 437

The Senate has passed a bill that would expand the number of seats in the House of Representatives by two. One fully voting seat would go to the District of Columbia, which is heavily Democrat, and the other would go to the next state in line for expansion, which is currently Republican-leaning Utah. The bill passed 61 to 37.

After reapportionment based on the 2010 census, the non-DC seat could go to a different state, but for now the addition of the two states is likely a wash. The WaPo says the number of House seats has not been increased since 1913, one year after Arizona and New Mexico became states. Alaska's and Hawaii's admission to the Union in 1959 did not change the House numbers (but of course, two Senate seats were added for each of the "freak states"). 

Were the territory of Guam and/or the Commonwealth of the Northern Mariana Islands (which includes Saipan) to get Statehood, something similar to 1959 would likely take place. If the Commonwealth of Puerto Rico, with four million residents, were to become a state, not providing for additional House members would mean several states would have to take a hit.

There will probably be challenges, and they could go all the way to the Supreme Court. Republicans opposed to the measure say that it is the "people of the several states" who, according to the Constitution, are to choose who sits in the House. Another problem is that the Senate version of the bill also seriously curtails gun ownership, while the House version does not.

This bill would not affect the Electoral College that picks the President, since the District of Columbia already has electoral votes that would be based on its membership in the House and Senate if it were a state (that number is now three).