If Mae West’s famous adage applies to American voters, Democrats should sweep the 2008 elections — if they don’t blow it.

The adage, of course, is: “When caught between two evils, I pick the one I haven’t tried before.” [IMGCAP(1)]

The evil Americans haven’t tried in a while — since 1994, in fact — is Democratic rule of both the White House and Congress.

Divided government worked reasonably well in 1995 and 1996, when Bill Clinton was president and Republicans ruled Congress, producing a balanced budget and welfare reform.

But it also produced a government shutdown and the fiasco of Clinton’s impeachment, which hurt Republicans but didn’t prevent them from keeping control of the House and capturing the White House in 2000.

Americans have tried all-Republican rule for most of the Bush years — except from 2001 to 2002, when Democrats controlled the Senate — but they demonstrated in the 2006 Congressional elections that they were fed up with that arrangement.

The political climate definitely favors Democrats winning back the White House and keeping control of Congress in 2008 — if they don’t squander their advantage by ideological overreaching or incompetence.

The latest Gallup Poll showed that, by 51 percent to 38 percent, voters prefer to see the White House go Democratic and the likeliest Democratic nominees now beat the likeliest Republicans in head-to-head matchups.

The warning for Democratic candidates lies in the closeness of some of those matchups. Democratic frontrunner Sen. Hillary Rodham Clinton (N.Y.) outpolls former Massachusetts Gov. Mitt Romney (R) by nearly 12 points in the latest RealClearPolitics.com average of recent surveys and beats former Sen. Fred Thompson (R-Tenn.) by 6 points.

But she runs ahead of former New York Mayor Rudy Giuliani by just 2 points and Sen. John McCain (Ariz.) by just 3.5 points, suggesting that if Republicans have the wit to nominate a candidate with appeal to independent voters, they can retain the White House in 2008.

RealClearPolitics’ averages show Democratic Sen. Barrack Obama (Ill.) running ahead of Thompson by nearly 10 points; Romney by nearly 17 points and McCain by 6 points, but leading Giuliani by 1.2 points, a statistical tie.

Former Sen. John Edwards (D-N.C.) leads Giuliani by 3.5, McCain by 8 and Romney by a whopping 22.6 points. For some reason, Edwards hasn’t been matched against Thompson.

Meanwhile, Democrats ought to be able to retain narrow control of the Senate with 22 GOP seats in play against only 12 for Democrats. Perhaps three Democratic Senators are truly vulnerable, while four or more GOP seats are in that category and retirements could produce more.

Democratic election experts are fairly confident that their party can retain its House majority, currently 16 seats. “It would take a national trend the other way to turn us out,” one of them told me, “and there’s nothing in the polls indicating that’s happening.”

Indeed, a Democracy Corps poll of 70 House districts showed Democrats well ahead in all Democratic districts and tied in competitive suburban, rural and urban GOP districts.

It’s true that Congress’ approval ratings are dismal — at 24 percent, according to Gallup, 8 points below President Bush — and that confidence in Congress as an institution is at 14 percent, a record low.

On the other hand, Gallup’s latest poll shows that respect for practically every institution — except the military and small business — is at record lows, including the presidency, public schools, the Supreme Court, big business, the media and even churches.

Americans are in a foul mood, as befits a country in the midst of an unpopular war. Public satisfaction with the country’s condition is down to 24 percent, according to Gallup, its lowest level since 1993, although not its lowest ever. That was 12 percent in 1979, during the doldrums of President Jimmy Carter’s administration.

Such dissatisfaction suggests the public wants change above all — and a good opportunity for Democrats to take back the White House unless other factors intervene.

As former President Bill Clinton’s one-time pollster, Doug Schoen, writes in his new book, “The Power of the Vote,” “to win, candidates have to be where the voters are. Unfortunately, many Democrats are still too far to the left. History could not be clearer on the point: Democrats who win at the national level are the ones who are tough on security, fiscally conservative and responsive to people of faith.”

Schoen thinks Democrats will lose in 2008 if they nominate a candidate who favors a “cut and run” policy in Iraq and former Vice President Al Gore’s 2000 style of populism because conservatives still outnumber liberals in America, 30 percent to 20 percent.

Conservative activist Grover Norquist, meanwhile, thinks a Republican could win in 2008 by adopting French President Nicolas Sarkozy’s campaign model — distancing himself from Bush as Sarkozy did from former French President Jacques Chirac and then denouncing French Socialist nominee Segolene Royal as too far left.

Or, if Democrats nominate a candidate perceived as too left and Republicans pick a Bushian conservative, it might attract moderate Independent New York Mayor Michael Bloomberg into the race, probably cutting into the Democrat’s appeal to independent voters.

The bottom line — at least for now — is that voters want something different from the divisiveness of the Bush era. Democrats have a glorious opportunity to return to power — if they don’t offer up divisiveness as an alternative.