The main obstacle is his reluctance to run for president and his wife’s even stauncher opposition to a campaign. It’s definitely not impossible, and the thought of having a moderate Republican president in the 1990s is interesting idea to play with.
Winning a Republican primary would be a bit difficult - Bob Dole nearly lost for not being conservative enough. Polls at the time showed Dole leading Powell by 32% to 30%. In the general election, Powell’s personal appeal would go a long way against Clinton; an exit poll conducted on Election Day had Powell leading by 12% after Dole lost by 8.5%. While this lead would evaporate as Powell became viewed as a more partisan figure, many of Clinton’s attacks against Dole would not work on Powell. Even without running,
Powell’s approval rating went down from 71% to 62% between 1993 and 1995. Of course, you could easily use a Clinton-screw POD like the Monica’s Baby timeline did. There was also talk of Powell running as an independent, though I see this as less likely.
One poll I found had him in second (Clinton: 37%, Powell: 32%, Dole: 24%) while
another had him in third (Clinton: 34%, Dole: 29%, Powell: 27%). Roughly basing Powell’s support by state on his supporters’ 1992 preferences, the electoral map would look like this.
President Bill Clinton (D-AR) / Vice President Al Gore (D-TN): 401 EVs, 37%
General Colin Powell (I-NY) / Senator Warren Rudman (I-NH): 79 EVs, 32%
Senator Bob Dole (R-KS) / Former Secretary Jack Kemp (R-TX): 58 EVs, 24%
To summarize, Powell would not be a shoo-in for the Republican nomination but would be uniquely suited to defeat Clinton in the general election.
you could also have the hamilton electors from 2016 somehow pull off a deadlocked election and get the house dems and a few republicans to vote for powell