An election with an incumbent is foremost a referendum on the performance of the incumbent.
Generally speaking, incumbents stand good chances to win reelection. In the U.S. midterms last year, all incumbent senators running for reelection prevailed on election day. At the presidential level, Donald Trump was the first incumbent president to lose reelection in almost thirty years.
The reason for this is that incumbents enjoy several distinct advantages. They most often have universal awareness and unique fundraising capabilities. An incumbent also has opportunities to get media attention and to set the agenda. As for myself, I have only ever lost one incumbent race, a state legislator in my early days in the trenches.
There is usually a specific thing that got incumbents elected in the first place. Call it a mandate. Incumbents should be seen as delivering on the mandate quickly after taking office. As new issues arise on the political horizon, an incumbent then has to reinvent himself and be seen addressing those concerns as well.
If an incumbent is doing his work properly with respect to politics, policy, and communication, he should sail to an easy reelection. The flip side to that is that if an incumbent has a tough race running for reelection, something went wrong during the time in office.
That said, a reelection campaign is different from a challenger campaign. Time has passed, the electorate has changed, there is probably a new opponent, and most importantly, the incumbent himself has changed. He went from being a challenger candidate that is free to criticize to being an incumbent with a record to defend.
While great campaigns should never be a rerun of previous good campaigns, this is particularly true for an incumbent running for reelection.
If you’re looking for a model on how to lose reelection, Donald Trump and Jair Bolsonaro are good examples. Both first won due to very particular circumstances. In the U.S., the unique electoral system allowed Trump to get elected in 2016 while getting less votes than his opponent. In the Brazilian election 2018, the most winnable candidate was not allowed to run and on election day, Bolsonaro was the last man standing.
Once in office, Trump and Bolsonaro both spent much of their time deliberately antagonizing the voters that had not voted for them. In the case of Trump, this was actually the majority of voters. Instead of reaching out and reinventing themselves, they doubled down and almost exclusively appealed to their respective base. In fairness, it’s thanks to their enthusiastic supporters that they came surprisingly close to winning a second term. If they would have reached out just a little bit, however, I think that both would still be in office today.
Courting swing voters and independents has become somewhat less trendy in recent years. Wrongly so. They are often the ones who decide an election.