We know that sounds obvious, but bear with us for a moment.

Yesterday we said Hillary Clinton would be a better opponent from John McCain’s perspective, as he could unite Republicans against her.

But that doesn’t mean a McCain-Barack Obama race wouldn’t get combative - or force voters to grapple with provocative policy issues.

It would be perhaps the most compelling race in history.

After splitting hairs between “good-enough” candidates for so long, America would not know where to start with this matchup. The Chicago Tribune throws out a few ideological debates we’d see:

• Will Barack’s guarantee of eligibility for any health care, expansion of Medicaid, and generally bigger government seem necessary? Or are John McCain’s ideas - portable coverage, efforts at cost control and compensation of providers - more reasonable?

• Are John McCain’s support for the Bush tax cuts, repealing the alternative minimum tax and all but killing the estate tax fuel for massive deficits? Are Obama’s calls to reduce the cuts, keep an estate tax and raise capital gains taxes classic Democratic foibles?

• Would McCain be seen as the military visionary whose call for a troop surge defined the way to win the Iraq war? Or would Barack Obama be vindicated as the only war opponent from the start, and whose policy of withdrawal looks like the only way to wind down what has become an interminable quagmire?