Voters generally like debates because they are a rare opportunity to see and compare candidates directly next to each other. There have however always been candidates who refused to debate, and then went on winning the election. When Tony Blair ran for Prime Minister of the UK, for example, he turned down a debate with incumbent John Major. French President Jacques Chirac refused to debate his opponent in the second round of the 2002 election, Jean-Marie Le Pen.
If candidates agree to a debate, they should take debate prep very seriously. This usually starts with the definition of the strategic goals to accomplish. If you do not know what your goal is, how can you assess how the debate went? If a candidate is fifteen percentage points ahead, the goal might be to simply not do to anything that changes that situation. And nothing more. Other strategic goals could be to address a certain weakness, to show another side of your candidacy, pivot away from a certain issue or allegation, stop the bleeding related to a certain scandal, create a certain controversy, or to get a certain message across. Effective debaters know what they want to accomplish strategically with a debate and have a plan on how to get there.
Ideally, they conduct several dry runs at the exact time and with the same format as the real debate will be. Allies play the role of the other candidates. You might remember the debates during the last U.S. presidential election when Donald Trump constantly interrupted and insulted Joe Biden. I am sure that Atty. Bob Bauer who apparently played Donald Trump in Biden’s mock debate, acted the exact same way.
You might also remember the 2010 U.S. presidential debates. Mitt Romney is not a particularly gifted speaker but won a surprise win against incumbent president Barack Obama, a great public speaker. Romney had conducted ten mock debates prior to the real one.
Read my comments on presidential debates in the Korea Times here.