1) Politics isn't about doing what you think is right and should win if the universe was fair and being willing to risk all your power if you are wrong. Politics is about making smart decisions that allow you to MAXIMIZE your ability to influence the outcome towards what you think is right. Obama and more importantly his supporters don't understand this. They will want to make everything right and be willing to go for broke on each issue. The problem with going for broke on a large number of issues is that eventually you do end up broke. If you notice thats EXACTLY what happened to Bush and the GOP. How many issues did Bush go for broke on? Taxes, social security, patriot act, Anti-electrical regulation in california, Iraq War, Terror, Stem cells, Torture, Justices, Immigration, Religion in science,
Support for Israel, Globalization etc etc etc. Obviously we need to roll back the Bush crap but Obama and more importantly his supporters want to literally be the anti-Bush and make the same mistakes on the other side which will ruin the party.
2) Obama will support foolish and unpopular ideas in his quest to be progressive and true to himself. Opposing the war in Iraq was VERY unpopular in 2002, history as we understand it today has broken Obama's way for the moment. However history as we understood it after we took Baghdad was very different. Obama was not intrinsically right on the war issue in a political sense, rather the tactical stupidity of the Bush team to not invest the troop count they needed and not have the infrastructure planning needed caused the war to be unpopular. Had Bush Jr mounted a smart tactical war like Bush Sr did Obama's career would have been almost over and Democrats had they joined him would have no political capital to resist the attack on social security, the patriot act, torture, loss of civil rights etc. A party can't afford to be a risk taker with 20 years of legacy over and over again based on one man.
3) Clinton and Obama have very different backers. Clinton is backed from the traditional democratic party, people who for better or worse have come out to support the party for decades, insiders, poor, women, hispanics, asians, but all DEMOCRATS with non radical individual agendas. Obama has a very fragile anti-Bush coalition of greens, "progressives", youth, blacks, rich liberals, libertarian, gop etc. Bush Jr also had a fragile coalition of religious conservatives, Arab Americans, Hispanics, Moderates etc but couldn't keep them together once it was clear that what the conservatives wanted was to kick out the hispanics and declare war on the Arabs etc. Obama has the same problem with his coalition, the change they want is not the same change.
The Bush disaster has shifted the balance of power to the Democrats. Possibly for the next 20 years. McCain winning the GOP nomination signals a loss of power of the far right. An Obama win would ease this shift because he will be the liberal Bush and make giant tactical mistakes that hurt his party.
Being right on the war isn't enough. Bush was right on appointing Blacks into his administration and courting Abab and Muslims in 2000 and cold have made serious inroads into that voting segment if it wasn't for all the other things he fucked up.
Being right on one issue isn't enough if you are always ready to risk it all on the next issue. Because eventually you lose and its only the smart, insider, will do anything, changes to match what people want politicians that survive. What Obama's supporters hate about Hillary is exactly what makes her more able to deliver positive change.