But Sanders’s 2016 success could also be the makings of his greatest 2020 challenge. When he entered the race in 2015, it was in large part to push his progressive left ideas. Other politicians picked up on the fact that Democratic voters liked the big ideas that Sanders was selling, and now the 2020 field is packed with contenders who are campaigning on platforms similar to his 2016 campaign. Sanders’s 2017 “Medicare for all” bill became something of a litmus test for those senators considering a 2020 run — Kamala Harris, Cory Booker, Kirsten Gillibrand and Elizabeth Warren all signed on as co-sponsors. Even Clinton acknowledged the appeal in her campaign memoir, “What Happened”: “I have a new appreciation for the galvanizing power of big, simple ideas. I still think my health care and college plans were more achievable than Bernie’s and that his were fraught with problems, but they were easier to explain and understand, and that counts for a lot.”

This means the progressive-left lane in 2020 is quite a bit more crowded than it was in 2016, which is a problem for Sanders, albeit a problem that stems from his own success. Warren is perhaps his most direct ideological competition — she’s been a critic of American capitalism for decades, though unlike Sanders, she still calls herself a capitalist and a Democrat. She also hired his 2016 Iowa caucus director — inside baseball to be sure, but it’s worth paying attention to the campaigns Democratic operatives choose to work for this early on.

Another potential complexifier for Sanders is that many Democrats appear to be prioritizing “electability” over ideology in 2020.