So, every four years America holds a presidential election, and every second year in the middle of the presidency, what are called "midterm" elections are held to fill all 435 House seats and one-third of the Senate's 100.
Almost invariably, midterm elections produce gains for the party which does not control the White House and the 2006 midterms are expected to fit that mold.
The question is, how big will the swing be?
As it stands the Democrats need to add 15 seats to take control of the House and 6 seats to regain a majority in the Senate.
Recent national polls suggest their chances are good, but for a lot of reasons, the likelihood is the polls overstate reality and that President George Bush's Republicans will retain majorities in both houses of Congress.
Despite poor polls, unseating
Republicans will be a tough call
Writ large, there is little question, the American public's judgments of Bush and his Republican Congressional team are harshly negative.
Even after the recent arrests in the UK of suspected terrorist hi-jackers, Bush's approval ratings barely managed to nudge above the 40% mark, while consistent majorities have actively disapproved of his performance as president.
Generic questions about Democrat versus Republican candidacies produce consistent 10 to 20 point national preferences for the Democrats.
But political races are not run generically, and in one-on-one competitions, the spreads are rarely that large.
Add to that the fact that historically most American voters, no matter how they grumble about Congress, usually vote for the Congressperson they already have, and shifts in party predominance become even harder to pull off.
Two as yet unanswered questions may determine the outcome in November:
Will American disappointment with the Bush administration's policies - particularly in Iraq - translate into rejection of other Republicans at the polls?
At crunch time, most Americans
vote for the one they know
And will the Democrats find and articulate alternative policies that will convince voters they can be trusted with power?
Remember, American voters polled less than luke-warm about Bush's policies, including the war in Iraq, in 2004. But they re-elected the president anyway.
As a famous American maxim has it: "You can't beat something with nothing," and so far, polls suggest the Democrats failed to convince voters they have something clear and consistent to define their programs for the future.
Take, for example, the question of Iraq.
Much of the Democratic "base", the party's most loyal voters and active campaign volunteers, hate the Bush administration's policies, and want a simple reversal of course: an exit strategy complete with a timeline for withdrawal of American troops.
These were the people most responsible for the recent party primary vote in the state of Connecticut, where 18 year incumbent Senator Joseph Lieberman lost his Democratic party nomination to an all-but-unknown anti-war candidate Ned Lamont.
Lieberman felt voters' wrath over
his support for the war in Iraq
The vote was close, but the 52-48% margin was clear.
But who is the most likely next Senator from Connecticut? None other than the very same Joseph Lieberman.
He is running in the November general election as an independent, and statewide polls show that - despite his status as perhaps the Democrats most unrestrained supporter of the Iraq war - he remains 10 to 12 points ahead of Lamont, whose one-note candidacy has attracted little support beyond his "anti-war base".
Republican strategists hope the Connecticut results will demonstrate their strength with voters as "tougher on terrorism" than the Democrats. Most national polls show this as the Republicans' best issue.
Anti-war feeling looks unlikely to
alter the balance in congress
Democratic hopefuls in other states, studying the complexities of Connecticut, wonder what to do.
Even in that relatively Liberal state, simply opposing the war does not seem enough to win the November election.
Some are finding other campaign issues.
- In Missouri, Democrat Claire McCaskill is emphasizing her support for stem cell research, something her Republican opponent, Senator Jim Talent opposes.
- In Montana and Ohio, Democrats are hoping to unseat 2 more Republican incumbents by underscoring their alleged ties to the convicted corrupt Republican lobbyist Jack Abramoff.
- While in hotly contested races in Pennsylvania, incumbents like Senator Rick Santorum and Congressman Curt Weldon are being asked to defend unpopular Bush policies from Iraq, health care and the environment to tax cuts for the wealthy.
In all these races, the Democrats are given good chances at success, but few expect them to win them all, as they will need to, to transform the Congress.
Usually, the lower the pre-election poll ratings of Congressional performance, the greater the displacement of incumbents on Election Day.
Poor polls over the Iraq war did
not stop Bush's 2004 re-election
Here again, the statistics seem to be on the side of the Democrats.
A recent Gallup poll put the national approval of Congress at just 27%.
Historically, when that number sinks below 40%, an average of 29 seats change parties, more than enough to propel the Democrats to power.
In 2004 however, notwithstanding their disappointment with Bush, voters showed little enthusiasm for John Kerry, the Democrat challenger.
And as the next round of mid-terms approach, there are few signs of voter passion for Congressional Democrats, despite plenty of evidence that popular disagreement with Republican policies has only grown in the past two years.
The Democrats face a tough fight if they are to avoid being stuck in the minority in both the House and the Senate in 2007.