Divided government is nothing new - in fact, it has long been the rule in Washington rather than the exception. What is new is the political polarization that has deepened since the last short spell of unity between the White House and Capitol Hill. That was broken when the Republicans won a majority in the House of Representatives four years ago.
President Barack Obama famously described that result as a "shellacking" at the time, and it had a major impact on his presidency. For Thomas E. Mann, a constitutional scholar at Washington's Brookings Institution, the Republican-controlled House of Representatives "effectively stopped any real opportunities to deal with problems through legislation."
Against that backdrop, losing the Senate would "merely add to the blockage on Capitol Hill," Mann told DW. One way around the blockage for the president is executive action - drawing on his own powers without the need for congressional approval. Obama is lining up such action on immigration and climate change.
But he can't count on success. As Cameron Seward of the conservative Heritage Foundation told DW, Republican leaders may wield Congress' "power of the purse … de-funding, cutting spending or maybe stopping spending on certain initiatives that the president undertakes through the executive branch."
And they have threatened to go further, with House Speaker John Boehner even raising the prospect of suing the president for overstepping his powers. Boehner has so far failed to follow through on that threat, but executive action has other vulnerabilities. As Mann points out, "any sort of executive orders can be overturned by a new administration."
ER for Obamacare?
Republicans are also expected to use their congressional strength to target the Obama administration's flagship achievement: the Affordable Care Act, the health care reform otherwise known as Obamacare. Senator Mitch McConnell, set to become Senate majority leader barring an upset in his own state of Kentucky, recently expressed determination to repeal the legislation. But without a supermajority of 60 seats in the Senate - required to override a filibuster by Democrats - he lacks the means to do so.
At most the Republicans might be able to chip away at some elements of the reform, such as a tax on medical devices, according to Mann. "You can fight sort of a guerilla war against existing laws: a form of nullification by not confirming appointees to run agencies, by cutting budgets down, by new aggressive oversight. But the act will not be repealed, it will still be law. It is gradually becoming a part of the American economy and society."
One area where the Republicans will be able to leverage their position in Congress is appointments to the Supreme Court - which are subject to confirmation in the Senate. With four Supreme Court Justices now in their late 70s or early 80s, vacancies are a distinct possibility in the next two years - giving Republicans a say in who fills them.
The Republican agenda
What about the Republicans' own political agenda? Seward of the Heritage Foundation says the party will probably use its new position in Congress to advance policies on a host of issues, from energy to tax reform. He acknowledges that many of their moves are likely to run into a formidable obstacle: the presidential veto.
But he says that need not stop them: "I think that message still gets out there - which is that we stand for this or we stand for that, which is the ultimate goal - for laying the groundwork for a presidential race in 2016."
With both parties eyeing that much bigger election on the horizon, is there any scope for constructive engagement between the White House and a Republican Congress? Mann holds out some hope on the issue of free trade, natural Republican territory.
The Obama administration is trying to negotiate massive free trade deals with Europe (Transatlantic Trade and Investment Partnership - TTIP) and the Asia-Pacific region (Trans-Pacific Partnership - TPP); many Democrats are skeptical. "In some respects having a Republican majority leader in the Senate may move this along more quickly than having [current Democrat majority leader] Harry Reid," said Mann.
But the overall outlook appears to be continued deadlock, with Congress and the White House blocking each other's every move while the respective parties gear up for the 2016 election.
And what about the rancor that has come to dominate the political discourse? For Dan Holler of Heritage Action for America, the ball is in the voters' court. He told reporters at a pre-election briefing, "this divisiveness will continue until the voters decide what they want. Right now, they don't seem to know what they want from Washington."
Mann, who has observed US politics for more than four decades, is pessimistic. "It's hard to imagine it could get even worse, but it probably will," he said. "It's good and evil, it's black and white - and behind all that are serious divisions over race, over religion, over the role of government. We really are a nation that has drawn apart by party."