Here's a likely presidential scenario:

Barack Obama goes to the Denver Democratic convention beginning Aug. 25 with a few more delegates than Hillary Clinton. At present, Obama leads in the delegate hunt by 1,617-1,498. Amid much discord and much controversy about the non-elected super delegates, Obama is nominated. Blacks and white liberals are ecstatic. Obama proclaims the "end of racism."

Critics, however, proclaim the end of the Democratic coalition. Huge numbers of Hispanics and working-class whites gasp and gag -- and resolve to vote Republican. They will not back a black candidate for president.

Likewise, huge numbers of Baby Boomer women, who crave a female president in their lifetime, are enraged that Obama has snuffed their dream. They contemplate the Eliot Spitzer sex scandal in New York, conclude that men are not capable of governance, and refuse to vote for any man for president.

As a result, John McCain wins the presidency, with the Republicans snatching victory from the jaws of defeat. But blacks are infuriated by Obama's loss, and America's so-called "racial divide," which Obama attempted to bridge, becomes a chasm. Blacks blame the Clintons for Obama's loss and determine to win with Obama in 2012. Hispanics and many whites feel increasingly uncomfortable in the Democratic Party.

Here's another:

The "Clinton Machine" pulls the proverbial rabbit out of the hat, and a majority of the 850 super delegates opt for Hillary. Despite amassing fewer elected delegates and fewer total primary votes than Obama, Clinton is nominated. Blacks and liberals are apoplectic at what becomes the "stolen nomination." Blacks boycott the election. McCain wins.

And yet another scenario:

After more than a year of incessant drivel about "change," a majority of the voters finally conclude that the prickly, iconoclastic McCain is a change -- but one well within their comfort zone. Voters decide that he has character and principles. Voters decide that he is an acceptable, unconventional Republican. Votes decide that he won't be a George Bush third term. McCain is the non-Bush, and far less upsetting to the status quo than Obama.

After the media, especially right-wing talk radio, pound Obama for months for his guilt-by-association with assorted "black racists" and extreme liberal clergy, the country -- especially working class whites and Hispanics -- decide that McCain, a decorated Vietnam veteran and prisoner of war, is a safe but unorthodox Republican and is preferred over a liberal -- if not radical -- Democrat such as Obama. McCain wins.

Here's a corollary scenario:

In a racially tinged environment, Republicans rebound smartly in Senate and House races. Democratic candidates either embrace Obama or equivocate. Either way, anti-Obama whites and Hispanics abandon all Democrats associated with Obama. Contrary to expectations, particularly given the domestic economic situation and the intractability of the Iraq War, Republicans gain seats in the U.S. House but lose a few Senate seats.

And then there are post-election scenarios:

Republican pessimists fear that McCain, if elected, will be ineffectual, that the economy will go into a recession, that Iraq will be unresolved, that the Democrats will score a huge win in the 2010 congressional election, and that McCain will leave office in 2012 as a failure -- another Millard Fillmore or William Howard Taft.

But Republican optimists have a contrary view. They believe McCain will be the next Ronald Reagan, successful in solving problems and able to build a cult of popularity around himself. To be sure, McCain is likable. The country is moving to the left, so the job of a shrewd Republican president is to be perceived as a "reformer" while maintaining the status quo. If president, McCain would have 4 years to reinvigorate the economy and get U.S. troops out of Iraq.

If he doesn't succeed the Republicans will get the blame, and they will suffer in the 2010 congressional elections -- much as Reagan was repudiated in the 1982 elections, and a discredited McCain will lose if he runs for re-election in 2012.

But if McCain is successful, a "Reagan Revolution" will occur. He will heal the breach of Hispanics from the Republicans -- due to both his immigration policies and to a black takeover of the Democratic Party. He will temper the fury engendered by the Iraq War. He will make everybody forget Bush.

In defeat, Obama will be defiant, and black Democrats and white liberals will be inflamed and determined to elect Obama in 2012. As a result, conservative white Democrats and Hispanics will feel increasingly estranged, and they will gravitate toward the Republicans. The 2012 election could see a resounding ratification of the McCain presidency, a political realignment, and the onset of another period of Republican dominance.

The key to most elections is the so-called "floaters," the 10 to 15 percent of voters who are political moderates, unaligned with either party, and generally apolitical. As 40 to 45 percent of the electorate are hard-core conservatives and Republicans and a like number are liberals and Democrats, the floaters are critical. To win the presidency, a contender usually must build a right-center or left-center coalition, winning a majority of the floaters.

In 2004 Bush and his strategist, Karl Rove, chose a different tact. They decided to broaden their base, not build a coalition. Bush lost the popular vote to Al Gore in 2000 by 50,996,116-50,456,169, or 48.4 percent to 47.8 percent, with 2,831,066 votes for Ralph Nader, but won by an electoral vote of 271-266. Bush won by 62,040,606 (50.7 percent) to 59,028,109 (48.3 percent) over John Kerry in 2004, with an electoral vote of 286-252. In 4 years the anti-Bush vote increased by 5,200,927 but the pro-Bush vote increased by 11,584,437.

Going into 2008 the Republican base, disillusioned with Bush in particular and Republicans in general, will diminish by at least 10 to 15 percent, back to the 2000 level, so to win McCain must (l) build a majority coalition that encompasses five million to 10 million 2004 Kerry voters or (2) run against a Democratic nominee who is so flawed that five million-plus Kerry backers won't vote for him or her.

McCain's potential problem is that some pro-Bush Republicans might vote against him or not vote at all. McCain voted against the 2001 and 2003 Bush tax cuts, sponsored the McCain-Feingold campaign finance reforms, opposed oil drilling in Alaska, supported amnesty for illegal aliens after paying a fine, backed stem cell research funding, backed a tobacco tax hike, opposed a constitutional amendment to ban abortion (although he is pro-life), opposed repealing the death tax, and denounced the use of waterboarding as an interrogation technique. That record certainly inoculates him from being called "Bush III." McCain is certainly different from the run-of-the-mill Republican, and he is almost a liberal -- or, as he will claim, an "independent" Republican. That will be what it takes for a Republican to win in 2008.

Of course, McCain claims to be an author of the "surge" strategy in Iraq, which has been successful, and he has no timetable for troop withdrawal. McCain loudly demanded Defense Secretary Don Rumsfeld's resignation, but he is still tied to the Bush position on Iraq. Obama wants to bring the U.S. troops home. If the election is a referendum on Iraq, Obama has an edge.

But if the election becomes a referendum on Obama -- which means it's about his race and his liberalism -- then McCain has the edge. That's where the "pouters" replace the floaters. Obama wants to be the bi-racial or post-racial candidate, sort of like the Tiger Woods of politics. Following the publicity over the comments of the Reverend Jeremiah Wright, Obama's pastor at the Hyde Park Trinity United Church of Christ, the senator acknowledged that there is a "chasm of misunderstanding" between the races and that both black and white "anger is real." Obama has been a parishioner for 20 years, and Wright has been the church's pastor for 36, but Obama claims he never heard Wright utter the phrases "United States of White America" or "not God bless America but God damn America." Wright believes that the country is "racist."

Obama is a smart, disciplined, calculating politician. His claim that "Generation Obama" is the "next great generation" smacks of conceit, and the primary results to date spell his doom: In southern states with a majority black Democratic turnout, Obama wins (but Georgia, South Carolina and Louisiana will go Republican in the election). In states with a high-income, liberal white majority (Vermont, Wisconsin, Washington), Obama wins, but in states with a black minority and working class whites (Ohio, New Jersey, Texas and likely Pennsylvania), Obama loses.

Democratic turnout has been phenomenally high in the 2008 presidential primaries, but the animosity between the black/white liberal Obama base and the working class/Hispanic Clinton base can be bridged only if the 2008 election is a referendum on Bush. McCain -- and the news media -- will make it all about Obama, and enough pouting Clinton Democrats will defect to enable McCain to win.