I would say he would be possibly the Republican nominee in 2008 or 2012
Actually, if Allen's in the race & cuts into Huckabee's vote total, then his presence can probably propel Romney to victory in Iowa. So, in this scenario, perhaps it's Romney who gets the nomination.
Possibly, but the problem for Romney is that Allen's base is similar to that of Fred Thompson's potential base (ie Conservative) suburbs, places like Atlanta metro that Romney ended up winning would almost certainly unite behind Allen. Thompson turned out to be a dud and later just a stalking horse for McCain to cut into Huckabee's support in Iowa and South Carolina.
Allen's collapse is what made possible Romney's opening as the "Conservative/Non-Populist" alternative to the McCain/Rudy. Allen takes Romney's base in most places and yes eats into Huckabee's support and probably ends up the nominee.
Remember Huckabee attacked the Club for Growth, said Bush had a bunker mentality on Iraq, openly talked about casting off fiscal conservatives from the coalition, had raised taxes as Governor of Arkansas and also passed instate tuition for illegals. Romney was not in a position to credibly nuke Huckabee owing to his own background in business and in Massachusetts. Allen, had no such problems.
That said, Allen would have had a big problem in a general election and I said it at the time to anyone who would listen, that the only way the GOP would retain the White House was with a businessman/non-Washington insider (no ties to Bush), who is seen as being culturally northern instead of Southern. We didn't talk in terms of non-college and college whites back then, it was just Northern and Southern, socially moderate and religious conservative, but ironically that same criteria that at the time pointed to Romney, accounts for Trump as well. The next GOP President was indeed a Businessman, from New York, with no political experience or ties to Bush.
Allen would have doubled down on the Southernization of the GOP, he literally wrapped himself in the confederate flag, and had voted with Bush 99% of the time. In a way, Allen's self-destruction was one that I welcomed at the time because it saved the GOP from a disaster waiting to happen, and I was already aware of Romney and was rooting for him to succeed.
