With Democrats poised today to significantly strengthen their majorities in the House and Senate, a historical review reveals that a political party’s control of Congress can be relatively long lasting — or not.

While House control has most recently seen a 12-year span for the Republicans and a 40-year tenure for the Democrats, political analysts and operatives on both sides of the aisle say this year’s projected large gains for the Democratic Party in the battle for Congress could easily begin to see a reversal in as little as two years.

Control of the Senate over the past half-century has proven somewhat softer than that of the House and since 1904, partisan command of either chamber has sometimes lasted for just one election cycle. Sen. Barack Obama (D-Ill.) is favored to win the White House today, and whomever the new president is could significantly impact how Democrats fare in their bid to retain control of Congress over the long term.

“We don’t know if this election is only a reaction to [President] Bush, or if it will turn into a more substantial realignment of voters,” said Stuart Rothenberg, editor of the Rothenberg Political Report and a columnist for Roll Call.

Most polls show Obama with a healthy lead over Sen. John McCain (R-Ariz.), including in a handful of states that usually vote Republican for president.

Prior to 1954, when Democrats took over the House for what turned out to be 40 years and the Senate for 26 years, Congress exhibited a penchant for volatile swings in partisan control. But even during those and other extended periods of a political party’s dominance over either chamber, there have been large gains for the minority, with even generally popular presidents finding themselves rebuffed by the voters in midterm years.

More Volatility a Century Ago

At the dawn of the 20th century, Republicans were still enjoying a cemented control of the House and Senate that had existed mostly uninterrupted since the end of the Civil War.

Republican control of the House continued beyond the 1904 elections — when President Theodore Roosevelt (R) was elected to a full term — through President Robert Taft’s (R) first and only midterm year in 1910, when the Democrats finally reclaimed the chamber with a gain of 56 seats. Republicans lost 10 Senate seats in 1910, but did not lose the chamber until Woodrow Wilson’s (D) election as president in 1912, when Democrats gained another nine seats.

Democratic control of the House ended abruptly in 1916 after just three cycles, with Republicans gaining 66 seats in Wilson’s first midterm year. Democratic control of the Senate also lasted only two cycles, with Republicans gaining six seats in 1918 — Wilson’s second midterm year.

Republicans maintained control of the House through the 1932 elections — eight cycles — when Franklin Delano Roosevelt (D) ascended to the White House. But even during those eight elections in which Democrats failed to reclaim the chamber, there were three cycles in which they gained seats and reduced the GOP majority, including 1922 (75 seats), 1926 (12 seats) and 1930 (53 seats).

During the 1918 to 1930 period that Republicans held the Senate, the Democrats still managed to pick up six seats in 1922, seven seats in 1926, and eight seats in 1930. The years 1922, 1926 and 1930 were midterm years for Republican presidents, with the 1930 election occurring right after the onset of the Great Depression.

Political analysts and both Democratic and Republican campaign operatives tend to agree that the most important factors determining partisan control of Congress are the image of the sitting president and the parties’ financial resources. However, some argue that how a majority party behaves in Congress during times of scandal is equally important.

If voters feel good about the president, his party usually benefits in House and Senate races — or at least isn’t punished to the point of losing its hold on Congress. If one party has a decided advantage in campaign cash, its Congressional candidates are often better- positioned to gain House and Senate seats — or at least are prepared to withstand a push from the opposition.

“This year’s election has been a referendum on a president who has destroyed his own brand’s image. Everyone running on the ticket inevitably suffers. There is no escaping Bush’s negatives,” Republican consultant Dave Gilliard said. “The other factor is money.”

Gilliard is based in California. His first year as a political professional was 1982, when a now-fondly remembered President Ronald Reagan (R) saw his party lose 26 House seats in his first midterm year after the economy failed to rebound during his first two years in office.

That followed a gain of 33 House seats for the Republicans in 1980 — many of them won on the strength of Reagan’s coattails. Reagan’s updraft also lifted 12 Republican Senate candidates to victory in 1980, allowing the GOP to take control of that chamber for the first time in 26 years.

Dismal Math for GOP

Congressional prognosticators predict the GOP could lose as many as 33 House seats and nine Senate seats today.

That’s not surprising, given the state of the presidential race and that Bush’s approval rating is cratering at about 25 percent nationally. Additionally, the Democrats have far more money to spend on Congressional races than do the Republicans.

Through Sunday, the Democratic Congressional Campaign Committee had outspent the National Republican Congressional Committee on independent expenditure advertising $77.2 million to $24.2 million. The Democratic Senatorial Campaign Committee also had outspent its GOP counterpart, pouring $58 million into IEs, compared to $36 million for the National Republican Senatorial Committee.

Political observers note that the business of politics has changed appreciably since the early 20th century, when Congressional control was marked with volatility and wild swings in each party’s hold on both House and Senate seats. But these observers also emphasize that many factors allowing for either party to control both chambers for decades at a time have been mitigated.

Modern adjustments to the political landscape that could impede a permanent majority are campaign-finance regulations, a multipronged, 24-hour news media, and Congressional ethics laws and rules eliminating many of the underhanded methods the majority party would use to maintain its dominance. Redistricting, while more scientific and therefore potentially more politically effective, might also see its influence wane as more states gravitate toward independent commissions.

Democratic consultant Tom Lindenfeld, who is based in Washington, D.C., said the current political climate and the concerns of voters make the Democratic agenda particularly more appealing than what’s being offered by the GOP this year.

But Lindenfeld, who got his start in politics working on then-Sen. George McGovern’s (D-S.D.) 1972 presidential campaign, said it would be incorrect to assume that the GOP won’t eventually regain its competitiveness. Lindenfeld suggested that the Republicans over time would rehabilitate their brand, cut into the Democrats’ resources advantage, and see the emergence of more compelling leaders.

“I definitely don’t believe that it’s a fait accompli that [Democratic control] is now locked in. I think the attachment of voters to Members isn’t so strong that it’s irreversible,” Lindenfeld said. “I think there’s a potential for malleability.”

Prior to the Republicans’ 1994-2006 run controlling the House, the Democrats ran the chamber for 40 years, beginning in 1954. From 1954 to 2006 — a 52-year span — control of the Senate flipped just six times.

In 1980, Republicans took over the Senate; six years later the Democrats reclaimed the chamber with an eight-seat gain, defeating many of the Republicans who were swept into office on Reagan’s coattails. In 1994, the Republicans retook the Senate on a gain of seven seats. Six years later, the chamber slipped into a tie on a Democratic gain of four seats, although Republicans maintained control thanks to Vice President Cheney’s tie-breaking vote.

A few months later in 2001, the Democrats regained control when then-Sen. Jim Jeffords (Vt.), a longtime Republican, became an Independent and switched his allegiance to the Democrats. In 2002, the Senate moved back into the Republican column with a GOP gain of two seats; and in 2006 it swung back to the Democrats when they gained six seats.

Minority Gains Even in Bleak Periods

Democrats will likely open the 111th Congress with their largest majorities at least since Bill Clinton won the presidency in 1992. That year, Democrats lost 10 House seats but still held a 258-176 majority. No Senate seats changed hands that election, allowing the Democrats to maintain their 57-43 advantage.

Even when one party has managed to hold onto Congress for years at a time, the minority has often eaten into the majority despite failing to win back the House, Senate or both.

During the 40 years that Democrats held the House, the Republicans picked up seats in nine elections, including gains of 20 seats in 1960 — when Democrat John F. Kennedy won the White House — 47 seats in 1966, 12 seats in 1972, 11 seats in 1978 and 14 seats in 1984.

The Republicans’ ability to begin eating into the Democrats’ majority in the next cycle and beyond will depend in large part on the president’s performance — at least initially. If Obama wins as expected and the public responds well to his administration, the GOP could be in for a difficult haul in the minority.

However, how well a Democratic White House is perceived could depend on its reaction to as-yet-unforeseen foreign and domestic crises — and how fast the GOP moves to recover on its own from what are expected to be big losses in today’s Congressional elections.

“It’s a combination of the Republicans starting to put together a message, and a combination of the president’s performance,” Rothenberg said.