I'll repeat....
Indicting, charging, arresting, trying, and even locking up political figures is absolutely nothing new in the US. Prominent examples include Vice President Spiro Agnew who was investigated, eventually pled guilty to tax evasion, and resigned; Rick Perry who was under indictment while running for President (case was eventually dismissed); and Johnathan Edwards who, similar to Trump, was investigated and indicted for covering up hush money payments (affair) he made during a Presidential campaign.
Of course this is the first time we've had an ex-President being indicted while running for election. But that's not very significant on its own for two reasons. First, being a "former President" offers zero protection from the justice system. The questions surrounding a sitting President can be quite complicated and involve lots of unresolved Constitutional issues, but once you leave office you're just a regular citizen, susceptible to being investigated, charged, and locked up the same as everyone else.
Second, given Trump's history, it's not like this is a surprise. Just in the last few years or so he was fined $25 million and his "university" was shut down because it was a fraud; the same is true of his "charity"; the Trump Organization was found guilty by a jury of a tax fraud scheme and his long-time accountant sent to federal prison; his National Security Advisor pled guilty to lying to the FBI; his Campaign Chair was convicted by a jury and sent to federal prison on fraud charges; his Deputy Campaign Chair went to federal prison as well; his personal lawyer was also sent to federal prison; his political advisor was convicted by a jury and sent to prison; his White House Senior Advisor was arrested on fraud charges; Trump himself was impeached twice.
So it's not like this potential indictment is coming out of nowhere. In fact, I'd say given the above, it was inevitable. The guy has always been a crook and surrounds himself with other crooks.