Kinda. Early in the 2016 election cycle, Jeb Bush was sort leading the pack. But, by October 2015 (to compare with the current cycle), Trump was pulling ahead in the GOP Primary and held onto the lead for the rest of the Primary. He was helped, a lot, by the large GOP Primary field and lack of a clear front runner. The political environment in 2016 also favored populism and Trump tapped into that very well.
Now, this could all get upended by the various criminal charges Trump faces. While the civil charges he is liable for are interesting, that’s not a real impediment to his campaign. Hell, I wouldn’t be surprised if that ends up helping him, as he will spin it as a politically motivated attack on him by the left. But, should Trump end up behind bars during the run up to the Primary or General election, that’s going to make campaigning a bit harder. It won’t be impossible, and I’m not entirely confident it would prevent him from winning the Primary or the General Election. Though, I would think that the GOP might find a way to replace him on the General Election ballot, were he behind bars.