When President Obama was elected in 2008, his victory signaled a generational change and the prospect of renewal for the Democratic Party. Instead, the opposite has occurred. Over the past six years, the party has been hollowed out.

The past two midterm elections have been cruel to Democrats, costing them control of the House and now the Senate, and producing a cumulative wipeout in the states. The 2010 and 2014 elections saw the defeat of younger politicians — some in office, others seeking it — who might have become national leaders.

As the post-Obama era nears, the Democrats’ best-known leaders in Washington are almost entirely from an older generation, from the vice presidency to most of the major leadership offices in the House and Senate. The generation-in-waiting will have to wait longer.

Presidential campaigns and open nomination contests help bring new leaders to national prominence. That appears unlikely in 2016. For all her positive attributes, former secretary of state Hillary Rodham Clinton is a suffocating presence when it comes to intraparty presidential competition. Her command of the Democratic machinery, from fundraising to grass-roots organizing, is so extensive that almost everyone else is understandably intimidated about even testing their talents against her.

Think of it this way: If Clinton were to win the presidency and serve two terms, the next opportunity for a new generation of Democrats to compete nationally would not come until 2024. The Democrats could go 16 years between competitive presidential nomination contests, wiping out opportunities for today’s younger generation to define or redefine the party apart from either the Obama or Clinton eras.

Texas Democratic gubernatorial candidate Wendy Davis makes her concession speech at her election watch party. The 2010 and 2014 elections saw the defeat of younger politicians — some in office, others seeking it — who might have become national leaders. (Tony Gutierrez/AP)

But don’t blame Clinton for these problems. The party’s national bench is so thin that Democrats count themselves lucky to have her available in 2016. If she were to decide not to run, the Democrats would have trouble identifying a field of candidates as extensive as Republicans are likely to put up in the coming presidential race.

The last competitive nomination campaign, in 2008, included — in addition to Obama and Clinton — an experienced field: then-senators Joe Biden, Christopher Dodd and John Edwards, and then-governor Bill Richardson. Clinton has been on the national stage for two decades. Biden, who might run if Clinton does not, was elected to the Senate four decades ago. Dodd and Richardson are out of office. Edwards is in disgrace. With the obvious exceptions, that field has disappeared.

Maryland Gov. Martin O’Malley has been moving toward a presidential candidacy. But he suffered a significant setback in Tuesday’s midterms when his state turned to Republican Larry Hogan to replace him. Sen. Bernard Sanders (I-Vt.) has a populist message for Democrats, but he is not going to be the party’s future. Sen. Elizabeth Warren of Massachusetts is a favorite of progressives and capable of stirring passions, but she shows no serious signs of running as long as Clinton is in the race, and perhaps even if Clinton isn’t.

The more serious problem for Democrats is the drubbing they’ve taken in the states, the breeding ground for future national talent and for policy experimentation. Republicans have unified control — the governorship and the legislature — in 23 states, according to the National Conference of State Legislatures. Democrats control just seven. Democrats hold 18 governorships, but only a handful are in the most populous states.

In California, Gov. Jerry Brown won again at age 76, his fourth, non-consecutive term in the governor’s office. His victory means that younger Democrats will have to wait until 2018 to compete for one of the nation’s most high-profile political jobs. In New York, Gov. Andrew M. Cuomo won a second term, but can’t get out of Clinton’s shadow. The only other state among the top 10 in population held by the Democrats is Pennsylvania, newly won by Tom Wolf.

Meanwhile, Republicans control governorships in Florida, Texas, Illinois, Ohio, Michigan, Wisconsin, North Carolina, Georgia and Massachusetts. Democrats were hoping to knock off Republicans Scott Walker in Wisconsin, Rick Scott in Florida and Rick Snyder in Michigan. All survived. In Ohio, John Kasich won by the second-largest margin in state history, thanks in part to the implosion of his Democratic opponent.

Ohio is an interesting case study of the fortunes of the two parties. It has been ground zero in presidential campaigns for years. Obama won it twice — but at the state level, Republicans are firmly in control. GOP candidates have won all the statewide elected offices there in five of the past six elections.

Without prominent statewide elected leaders, Democrats are in danger of seeing their state party structures atrophy. This has happened in Texas over the past two decades, ever since Republicans seized control of the politics of the state.

After years of neglect, Democrats found in Wendy Davis the kind of candidate they hoped would prove compelling enough to jump-start their revival. Instead she lost to Gov.-elect Greg Abbott by 20 points.

In Georgia — another state, like Texas, where Democrats see a changing population improving their prospects of winning statewide elections — Michelle Nunn ran what was considered a very good campaign for the Senate that appeared likely to end up in a runoff. She lost to David Perdue by eight points. And on and on.

There are talented Democrats in Washington, but in a Senate largely devoid of real debate or action, it’s difficult for them to gain a foothold nationally. They can have a presence on cable news and the Sunday talk shows. Now in the minority, some of them may speak with more independence. But they will have little opportunity to put their ideas into practice.

Since 2010, Republicans have showcased their governors’ conservative agendas. Some of those governors have felt the sting of a voter backlash against some of those policies. Yet other than in Pennsylvania, they all won again, carrying red, blue and purple states. Those who survived should learn from the scares they got this fall, making them more battle-tested and perhaps wiser in their second terms.

Meanwhile, Democrats were defeated in gubernatorial races in three blue states, losing an incumbent in Illinois and open races in Massachusetts and Maryland. Among their embattled incumbents, Connecticut’s Dan Malloy, a traditional Democrat, and Colorado’s John Hickenlooper, a nontraditional Democrat, survived. Hickenlooper, who eschewed negative ads in a year in which they came in buckets, actually won by a larger margin than did the GOP’s victorious Senate candidate, Rep. Cory Gardner.

The dearth of power in the states translates into a less vibrant policy debate within the Democratic Party at a time when Democrats need a bigger and more compelling economic message. Democrats ran tactical campaigns with tactical messaging this fall. Absent more governors, with the ability to test and refine programs, the party will have more difficulty developing fresh ideas. Everyone is counting on Clinton. But with whom will Clinton — if she runs — have a serious intraparty debate about the post-Obama agenda?

None of this means that Democrats will lose the presidential election in 2016. The coalition that Obama assembled to win in 2008 and 2012, to the degree that it remains intact, gives them a head start in a national campaign. As does the electoral map.

Those realities continue to worry many Republicans. Reince Priebus, the Republican National Committee chairman, told reporters at a Christian Science Monitor breakfast Friday: “A Democrat can be good and win [a national election]. We’ve got to be great.”

But a political party cannot be constructed around two individuals (Obama and Clinton), as Democrats seem to be today. Winning the presidency and taking back the Senate will be the Democrats’ top priorities in the next two years. The bigger challenge of rebuilding the party in the states and nurturing a new generation of leaders should be just as urgent.