An Obama-era decision ensured that the project will continue to receive money until 2024, a four-year extension at the time. But after that, its fate has always been up in the air. And it's an expensive place to visit: Every year, NASA spends between $3 and 4 billion on the space station, totaling about $87 billion since the project first began in 1993.
The argument behind killing the program isn't that it isn't fun, it's that all that money could be put toward more ambitious space goals, like putting humans on the moon or Mars. Last year, Congress and the president told NASA to work on a transition plan that would let the agency keep visiting the space station without racking up such hefty room service bills.
NASA already cut back on its space station funding in 2011 when it eliminated the space shuttle program and switched to renting out seats in Russian Soyuz capsules. It was hoping to be able to hitch a ride with commercial space corporations, but had to purchase more Soyuz flights for 2018 and 2019 after SpaceX and Boeing lagged in becoming certified.
The situation is complicated, of course, by the "international" bit of the ISS's name: The station is also owned and operated by Russia, 22 European countries, Japan, and Canada. The U.S. is the largest financial contributor, with the other countries involved throwing in a total of about $1 billion per year. According to The Verge, the rest of the ISS partners are also up in the air on anything past 2024.
Different countries have built out different sections of the space station, so for example, the kitchen is located in the Russian area—things might get messy if one country pulls out and the others try to keep the project going. Russia also manages the Soyuz program, which is currently the only way for astronauts to get to or from the space station.
If the space station program does end in 2025, we will still have sucked almost as much science out of the project as we can: NASA administrators think the station will need to be retired in 2028 anyway. Whenever that day comes, the ISS will be pulled out of space and buried in the Pacific Ocean—it's too dangerous to leave the corpse up there, no matter how expensive that corpse was to build.