If he had beaten GWB in the primaries and defeated Al Gore in the general how would his presidency have gone over that period? This is assuming that 9/11 would still happens (unless some think it wouldn't have?).
I'll reuse a post I just wrote on a similar thread:
He may have put greater pressure on the FBI and CIA to get Bin Laden and done more to prepare for an attack. If 9/11 still happens, he invades Afghanistan and focuses like a laser beam on getting Bin Laden. That said, the Iraq War unfortunately still happens. McCain advocated for war even earlier than Bush and he wanted Hussein gone. However, I feel that McCain would have liberated Iraq instead of occupying it as was the original plan. So the Iraqi army would still be intact and Iraq's basic social structures remain in place so the country is left relatively stable at least compared to OTL. He also would never have allowed the CIA to implement torture, for obvious reasons.
No Bush tax cuts, and we could see a cap-and-trade bill that Bush wanted before this was blocked by Cheney. I don't think McCain would have handled Katrina or the economic crisis very differently from Bush based on what I've read. In both cases he was reluctant to take action as it would have required high levels of federal spending and in the latter case interference in the economy. However he would show strong political leadership in both crises, whereas Bush looked like a deer in headlights much of the time.
IMO, it is better for McCain's legacy that he never became President. In OTL he is remembered for his wartime heroics and leadership as a US Senator. Had he been President during this time he would have taken the blame for Iraq, Katrina, and the Great Recession.
No Guantanamo Bay detention centre and no torture of prisoners in Afghanistan or elsewhere.
For those 2 reasons alone maybe his legacy even with an Iraq war would not have been as tarnished as Bush's.
I'm not convinced that President McCain will invade Iraq. He will not necessarily have the same advisors as GWB, some but not all and McCain will probably also be harder to sway. If nothing else he will ask tougher questions and demand concrete answers. It's possible he still goes through with it (it's possible Gore would have too) but definitely not a guarantee.
If McCain goes in, removes Saddam, but leaves the fundamental structure of the regime, Iraqi military, and broader society intact then the war might be seen positively.
If you have an Iraq War that goes well and McCain uses the Afghan War as an opportunity to improve relations with Iran, McCain would leave a very strong foreign policy legacy.
Although if he still bases the war on a lie and the UN considers him in violation of international law, that would damage his reputation.
Who is McCain's running mate? Likely somebody more conservative than himself who doesn't put off suburban moderates. Fred Thompson does the job and turns Tennessee into another front to campaign in. Otherwise, Liz Dole maybe? John Kasich the fiscal hawk from a swing state could work too perhaps.
Michigan Governor John Engler would be a plausible running mate. He could make the upper Midwest more competitive for the GOP ticket.
Pennsylvania Governor Tom Ridge would also be an option - in OTL he was supposedly on McCain's VP shortlist in 2008. The main problem with Ridge is that he's pro-choice, which would upset the religious right (who would already be lukewarm about 2000 McCain, especially given his denunciation of Pat Robertson and Jerry Falwell as "agents of intolerance").
However, McCain will play a lot stronger in suburbia and with independents. I think he wins Oregon and Wisconsin here. Florida will be safe for McCain as well, I think.
In such a TL, McCain wins decisively and unlike Dubya there aren't questions about his legitimacy. I wonder how Gore would be viewed in this universe. For a while he gained a lot of sympathy as someone who was cheated out of the Presidency, but here the blame would all be on him for losing in 2000.
I've never really understood why people think McCain would have been a stronger candidate than Bush in 2000. From what we saw of McCain's 2008 campaign, his campaign organization was horribly disorganized (witness their almost complete lack of vetting of Palin), and McCain's own campaign instincts were pretty poor. (Just consider him wanting to make Lieberman his veep or the bizarre decision to suspend his campaign and try to postpone one of the presidential debates.) Add in the fact that the 2000 election is going to be a domestic policy election (McCain's weakest area), and it's difficult to imagine McCain beating Gore in 2000.