Julian Castro is no Barack Obama. And for that, Democrats have themselves to blame.  The focus of this week's Democratic convention was President Obama. Lost in the adulation was the diminished state to which he has brought his broader party. Today's Democrats are a shadow of 2008—struggling for re-election, isolated to a handful of states, lacking reform ideas, bereft of a future political bench. It has been a stunning slide.  The speech by Mr. Castro, the young and charismatic mayor of San Antonio, was the Democrats' attempt to recapture the party optimism that then-Senate candidate Obama sparked at the 2004 convention. John Kerry didn't win, but that year marked the start of an ambitious Democratic plan to revitalize the party.  Democratic pollster Stan Greenberg on President Obama's recent decline in the polls and whether he'll get a bump from the convention. Credit: Associated Press  In 2006, Nancy Pelosi muzzled her liberal inclinations to recruit and elect her "Majority Makers"—a crop of moderate and conservative Democrats who won Republican districts and delivered control of the House for the first time in 14 years.  Democrats in 2006 also claimed the Senate, with savvy victories in states like Montana and Virginia. The party thumped Republicans in gubernatorial races, winning in the South (Arkansas), the Mountain West (Colorado), and in Ohio (for the first time since 1991). A vibrant candidate Obama further boosted Democratic ranks in 2008.  By 2009, President Obama presided over what could fairly be called a big-tent coalition. The Blue Dog caucus had swelled to 51 members, representing plenty of conservative America. Democrats held the majority of governorships. Mr. Obama had won historic victories in Virginia and North Carolina. The prediction of liberal demographers John Judis and Ruy Teixeira's 2004 book, "The Emerging Democratic Majority"—lasting progressive dominance via a coalition of minorities, women, suburbanites and professionals—attracted greater attention among political analysts.  It took Mr. Obama two years to destroy this potential, with an agenda that forced his party to field vote after debilitating vote—stimulus, ObamaCare, spending, climate change. The public backlash, combined with the president's mismanagement of the economy, has reversed Democrats' electoral gains and left a party smaller than at any time since the mid-1990s.  Of the 21 Blue Dogs elected since 2006, five remain in office. The caucus is on the verge of extinction, as members have retired, been defeated in primaries waged by liberal activists, or face impossible re-elections. The GOP is set to take Senate seats in North Dakota and Nebraska, and maybe to overturn Democratic toeholds in states from Montana to Virginia. There is today a GOP senator in Massachusetts. Republicans claim 29 governorships and may gain two to four more this year.  As for the presidential race, Republicans are in sight of taking back Virginia and North Carolina and are competitive in supposedly new Democratic strongholds like Colorado and New Mexico. The GOP is also making unexpected inroads in Wisconsin and Iowa. The real story of the Obama presidency is the degree to which he has pushed his party back toward its coastal and urban strongholds.  All this was vividly on display in Charlotte this week. While the party's most vulnerable members aren't in outright mutiny against Mr. Obama, more than two dozen didn't risk attending the convention. In contrast to last week's GOP celebration of reformist GOP governors, the Charlotte podium was largely dominated by activists (Sandra Fluke, Lilly Ledbetter), the liberal congressional faithful (Mrs. Pelosi, Harry Reid), and urban mayors from failing states (Los Angeles's Antonio Villaraigosa, Chicago's Rahm Emanuel).  San Antonio Mayor Julian Castro at the Democratic convention, Sept. 4.  While the GOP has feted its upcoming stars—including minority governors like New Mexico's Susana Martinez and Louisiana's Bobby Jindal—the president has done little to nurture his down-ballot partners. Where is the next generation of Democrats?  Which brings us to Mr. Castro. Mr. Obama lit up the political scene in 2004 with a lofty convention speech that told a heartfelt story, appealed to the best of America, and never once mentioned George W. Bush.  Mr. Castro, by contrast, was tasked by the Obama team with laying out the bitter Democratic themes of this election. His own eloquent story was weighed down by his job of ridiculing Mitt Romney, lauding government, and stoking class warfare. The comparisons of Mr. Castro in 2012 with Mr. Obama in 2004 are misplaced; Mr. Obama has made them impossible.  Mr. Castro must be wondering what chance he has of higher office in Texas, which today has not one statewide elected Democrat. It's a question for Democrats across wide sections of the country.  The liberals who supported Mr. Obama's expansion of the entitlement state are pinning everything on Mr. Obama's re-election, assuming it will cement their big-government gains and allow them to grind back congressional majorities in the future.  But contemplate the situation if he loses. Consider a Democratic Party that may hold neither the White House nor Congress, that has disappeared in parts of the country, and that has few future Obama-like stars. Compare that to 2008. This is the party Barack Obama un-built.  A version of this article appeared September 7, 2012, on page A13 in the U.S. edition of The Wall Street Journal, with the headline: The Party that Obama Un-Built.
In The Wall Street Journal, Potomac Watch columnist Kimberley Strassel writes that the Obama administration has diminished the ranks of elected Democrats in Congress and in state capitals across the country.