WASHINGTON (MarketWatch) — The election is over. The pomp and ceremony at the beginning of the new congressional session is finished. Now begins the harder task of governing.

But before the senators and representatives get down to business, they should recognize the difference between politics and policy making. Not everything that was said on the campaign trail should follow them to Washington.

Here are three things the new lawmakers need to know.

The Constitution was written to create a powerful, active central government.

Yes, I know that many in the conservative movement believe just the opposite, but they haven’t read their history. Their nostalgia is misplaced: They seem to pine for the weak government we had until 1787 under the Articles of Confederation, not the strong government established by the Constitution.

The framers of the Constitution believed the first central government we had after independence was too weak. And so they deliberately created a strong central government. Not a government with unlimited powers, but one that could effectively “promote the general welfare.”

The first Continental Congress didn’t have the power to tax, nor could it regulate commerce between the states or with the world. This weak central government was a disaster. It hindered economic growth and left the fledgling nation at risk of being gobbled up again by the European powers.

Read the Constitution if you don’t believe me. In particular, look at Section 8 of Article 1, which says that “The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States…” Read the Constitution.

If that authority wasn’t broad enough, the framers said Congress would have the power “to make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.”

We can surely disagree about how big our government should be, but that’s a question for the living to decide, not the dead. The dead have spoken: The Congress has the authority to impose taxes, to regulate commerce, and to do whatever is necessary and proper to create a more perfect union.

Federal spending has not surged permanently out of control

The federal deficit has soared to the highest levels since World War II, it’s true. In 2009, the federal deficit rose to $1.4 trillion, or 10.4% of gross domestic product. It’ll be huge again in 2011. But the main reason for the explosion in the deficit was the recession, not the growth of federal programs. Excluding the cyclical factors related to the recession, the structural deficit of the government in 2009 was the smallest since the government ran a surplus in 2001, according to the nonpartisan Congressional Budget Office.

The recession was incredibly costly. Government revenues plunged 5% in 2008 and another 17% in 2009, due to slower growth and the big tax cuts in the stimulus bill. The bank failures and bailouts added hundreds of billions of dollars in outlays. Unemployment benefits soared, as did spending on food stamps and other income security programs, spending that kept millions of Americans from destitution. The stimulus bill also spent hundreds of billions on infrastructure investments and in direct payments to the states to offset their falling revenues.

All that spending added up to huge and unsustainable deficits. But it was temporary spending. It was an emergency response, not the creation of new permanent programs.

The CBO figures that, under current law, overall federal spending in 2012 (the fourth year of President Barack Obama’s term) will be around 23% of GDP, nearly identical to what it was in Ronald Reagan’s fourth year as president.

We certainly have long-term budget challenges. We cannot keep spending far more than we collect in taxes. Both parties acknowledge that painful truth. But we can’t have an honest discussion about our long-term problems if we don’t understand how we got here.

Which leads us to our third inconvenient truth:

Tax cuts don’t pay for themselves

The victorious Republicans campaigned on balancing the budget and cutting taxes. They promised to implement tough new budget rules that would begin to turn the red ink into black. But a funny thing happened on the way to the Capitol: The Republicans decided that they’d like to cut taxes, even if doing so made the deficits worse.

They threw the promise to balance the budget under the bus the first chance they got.

In the House, the Republicans have adopted new rules that will ensure higher deficits in coming years. They’ve done away with the Democrats’ rules that require that any legislation that increases spending or lowers taxes must be offset by spending cuts or tax hikes elsewhere in the budget. These sorts of pay-go rules can be effective in controlling deficits, as long as they are enforced consistently.

Unfortunately, the Republicans carved out a huge exception that will make deficit reduction almost impossible. Under their rules, spending increases must be paid for, but tax cuts won’t. This is the same philosophy that added about $2 trillion to the deficit after the Bush tax cuts of 2001. The Republicans argue — against all logic and evidence — that cutting taxes doesn’t add to the deficit. Read more about debt ceiling debate.

To add insult to injury, the Republicans have carved out another exception in their very first floor vote, the bill to repeal the Democrats’ health-care reform law. Repealing the health-care law would add $230 billion to the deficit over the next 10 years, and would increase the federal deficit by about 0.5% of GDP in the years after 2022, adding another $1 trillion to the debt by 2030. See related story on health law repeal effort.

However, the Republicans will not enforce their own rules that would require that such spending increases be offset.

Drinking the Kool-Aid

We expect politicians to exaggerate, distort and mislead when they are campaigning. A 30-second ad is no place for nuance, or facts.

But once they get in office, we should expect them to remember the difference between politicking and reality. These people have our futures in their hands, and they shouldn’t be so ready to believe their own lies.