I have a simple mechanic that I think would do wonders to add flavor and balance out candidates like buttigieg; each candidate could have exactly one "attribute", which reflects certain real world traits, that modify their stats.
These traits could have a mixture of very negative and very positive impacts, or moderate or mild positive boosts.
Buttigieg: Dark Horse Darling; as a relatively unknown but broadly likeable candidate, this nominee gets every stat boosted by one level. However, enthusiasm over these candidates takes longer to build
+2 all attributes except wealth (minority appeal, etc), but initial enthusiasm starts at half of normal values, and grows at 3/4 the rate.
Trump: Twitter Politician(alt. "Unpredictable candidate); this candidate is known for making sudden, drastic changes and statements. When giving speeches, there is a 15% chance they choose a random topic and stance (whether available or not). Additionally, there is a 50% chance of this occurring during interviews. However, enthusiasm grows at a x3 rate, and does not decay.
Joe Biden: "Bland Candidate"; this candidate fails to excite, but rarely offends. They receive a high boost to all issue scores, but enthusiasm is capped at 80.
Bernie Sanders: Crowd Funded Campaign; by taking small donations, this candidate's speeches generate money similar to fundraising. Also, HQ income increases to 1.25x. However, running out of money, or actively fundraising severely penalizes them in almost every way (issue scores drop, enthusiasm resets).
Moderate candidate (I made john kasich): This candidate appeals to people in the middle. Undecideds generate enthusiasm for their party, and they receive a boost to all issue scores regardless of stance. However, speeches, HQs and ads generate 1/3 enthusiasm
Hillary Clinton: Mob Boss Politics; this candidate represents a style reminiscent of 19th century party bosses. They start with massive penalties to enthusiasm, and enthusiasm decays over time. HQs do not generate enthusiasm. However, they start with 3 free operatives, a free ideology pick and future operates are 50% cheaper
These are very rough ideas. I think it could be interesting to add! Each candidate would have to have one, and only one. But they could have dramatic impacts on playstyle which would add diversity to strategies.
Please add your own suggestions!