When Donald Trump takes the stand Monday in a Manhattan courtroom to testify in his civil fraud trial, it will be an undeniable spectacle. He'll be a former president and the leading Republican presidential candidate defending himself against allegations that he dramatically inflated his net worth. The charges cut to the very heart of the brand Trump spent decades carefully crafting and put him at risk of losing control of much of his business empire. But the appearance will also mark the beginning of what will likely be a defining feature of the 2024 election: a major candidate, on trial, using the witness stand as a campaign platform.