Barack Obama has said that he wants to help Democrats win back a majority in the House of Representatives. He says he looks forward to Nancy Pelosi being speaker again.

If he does work hard to elect House Democrats, it will be a change from 2010 and 2012, when he didn't do much at all for them.

But let's say he does. What are the chances of success?

Certainly not zero. Democrats need to gain 17 seats to win a House majority of 218. That's fewer than the number of seats that changed party in 2006, 2008 and 2010.

And let's not regard as etched in stone the Six Year Rule, which says that the president's party always loses lots of seats in the sixth year of his presidency.

That didn't happen in 1998, when Bill Clinton's Democrats actually picked up five seats. And in Ronald Reagan's sixth year in 1986, Democrats gained only five seats.

Which is to say, the Six Year Rule was inoperative in two of the three eight-year presidencies in the last 40 years.

Polling shows that voters have much more negative feelings toward congressional Republicans than congressional Democrats. Postelection polls have shown Democrats ahead of Republicans on the generic ballot -- which party's candidate for the House would you vote for?

All but one of those polls was conducted by Scott Rasmussen, most of whose polls before the 2012 election showed the parties about even in the generic ballot. Rasmussen's most recent survey shows the gap closing, but that's just one poll and could be statistical noise.

So there's a case to be made that the Democrats can win back the majority. But there's also a case to be made that they can't, or at least that it will be very hard.

The crux of that case is that the playing field favors the Republicans. Only 16 of the 234 House Republicans represent districts carried by Barack Obama.

That's because by the latest count I've seen (we're still waiting on a definitive tabulation of the presidential vote by congressional districts), Mitt Romney carried 228 congressional districts and Obama carried only 207.

Democrats attribute that to partisan Republican redistricting plans. That's a partial, but only a partial, explanation.

Republicans did protect many of their members in Florida, Michigan, Ohio and Pennsylvania and gained seats in North Carolina through redistricting. But redistricting plans gave Democrats offsetting gains in Arizona, California and Maryland.

What hurts the Democrats in any districting plan is the fact that the Obama Democratic constituency is geographically clustered.

Blacks, Hispanics and gentry liberals tend to live in densely populated urban areas that are hugely Democratic. You see the same effect on a smaller scale in university towns.

Republican voters are scarce in these areas but more evenly spread around in the rest of the country. You can find many 80 percent Democratic congressional districts. You'll have a hard time finding an 80 percent Republican one.

Here is one of the reasons the Six Year Rule often becomes relevant. In off-year elections, the president's party tends to be tethered to his record while the opposition party can field candidates adapted to the local terrain.

That's what House and Senate Democrats did under the inspired leadership of Rahm Emanuel and Chuck Schumer in 2006 and 2008.

George W. Bush carried 255 House districts in 2004. But in 2006 and 2008, he was unpopular, and a gun-totin', tobacco-chewin' Democrat could carry a rural or Southern Republican-leaning district. Many did.

Republicans may have a hard time doing that in 2014, because their primary voters sometimes prefer unelectable purist candidates over those adapted to the local terrain.

But Democrats will have a very hard time going local, because their party is largely defined by the man in the White House.

The outcome could hinge on events that have not happened and decisions that have not yet been made.

Job approval for Ronald Reagan and Bill Clinton in their sixth years was about 70 percent. The Six Year Rule didn't apply.

Obama's job approval is a little over 50 percent now. But this could rise, depending on events. That would improve Democrats' chances for a House majority.

But it could also fall or hover about where it is. In which case House Democrats' road to a majority is uphill.

Michael Barone,The Examiner's senior political analyst, can be contacted at mbarone@washingtonexaminer.com. His column appears Wednesday and Sunday, and his stories and blog posts appear on washingtonexaminer.com.