What’s this? For another three weeks, the Democrats control both chambers of Congress and the White House. But clearly the Republicans are running the country.

After years of planning for the end of the Bush-era tax cuts, the Obama administration in a matter of days came to an agreement to extend the tax cuts the Democrats first wanted to end, then were willing to extend only to the middle class and poor, and now have been persuaded to grant to every American. Do not say that elections do not have consequences.

The midterm congressional elections were more than a shellacking. Anyone who knows shellac knows that it covers only the surface of an object. What happened in the capital last week underlines that President Barack Obama actually was minimizing the transformation in American politics when he described the election results as a “shellacking.” The 2010 elections reached far deeper, into the very grains of American civic life.

In parliamentary systems, executives whose parties suffer what Obama’s did — the loss of the House, the loss of commanding advantage in the Senate and, less noticed but perhaps even more portentous, the loss of a record 680 seats in the nation’s state legislatures — swiftly resign or are removed from office.

Herbert Hoover, who knew something about repudiation, once said that democracy is not a polite employer. In fact, American democracy is a far more polite employer than the British or Canadian versions. Obama, like Ronald Reagan and Bill Clinton before him, gets to fight another day as president. Both the 40th and 42nd presidents used damaging midterm congressional elections — though they were far less disastrous than Obama’s — to tack away from danger and into the warm seas of re-election.

That’s Obama’s task for the year 2011.

The biggest midterm congressional election defeat in modern times came in 1938, when Franklin Roosevelt’s Democrats lost 71 House seats and six Senate seats. And that number understates FDR’s defeat, because Sens. Walter George of Georgia, Ellison D. “Cotton Ed” Smith of South Carolina and Millard Tydings of Maryland all survived, but as anti-New Deal Democrats.

Ordinarily, the 1938 midterms would have been his last and FDR would have been a lame-duck president, but Roosevelt chose to run again in 1940, when he won an unprecedented third term.

There is no question that the changed political landscape changed the Roosevelt presidency, just as it already has altered the Obama presidency. The 1938 campaign made FDR rethink his fiscal conservatism — a fiscal conservatism that some of Obama’s onetime allies on the left now worry has infected the current president. But like Obama, FDR faced a Congress that was far more conservative than it had been and that constrained him as he contemplated a Europe embroiled in tensions he knew would lead to war. Thus began a period of political deadlock that in many historians’ view lasted through 1964.

“With all of the talk about how badly the Obama Democrats did in the recent elections,” says William E. Leuchtenburg, one of FDR’s most distinguished biographers, “Roosevelt’s results were even worse.”

Presidents suffering from midterm blues necessarily adjust to a changed situation, often imitating their opponents while alienating their friends. Ronald Reagan wasn’t formally elected to the presidency until 1980 and didn’t propose his first budget until 1981, but I’ve always thought that Reagan ran the country for the last two years of the Jimmy Carter presidency.

Carter’s losses in the 1978 midterms were relatively benign — only 15 seats in the House and three in the Senate. Carter was a different president thereafter, as reflected in the budget he submitted for fiscal 1980, which he described as “lean and austere,” just the way Reagan would have liked it.

Clinton’s 1994 losses were more severe (52 seats in the House, eight in the Senate) and he reacted decisively. One result was the 1996 welfare overhaul, whose final form was shaped in personal negotiations involving the president and House Speaker Newt Gingrich, and was opposed, pointedly, by Health and Human Services Secretary Donna Shalala, who was responsible for welfare programs. All 21 votes against the bill in the Senate came from Democrats.

How the new Republican ascendancy will reshape the Obama presidency is the greatest mystery in American politics today, affecting not only the president’s re-election prospects in the 2012 elections but also the profile of the GOP as it prepares for the presidential election and for congressional elections in which the Democrats presumably will be on the defensive again.

But the Roosevelt, Carter and Clinton examples may be telling. Presidents rebuffed or under pressure domestically often turn to foreign policy, where their prerogatives are greater and their room to maneuver wider. FDR gave an increasing amount of attention to world affairs from 1939 on, as Reagan did in 1983 and Clinton did in 1995.

Obama traveled more in 2009 than any president in his first year. The voters’ verdict in his second year may shape his itinerary for his third year.

— David Shribman is executive editor of the Pittsburgh Post-Gazette.