Earlier this month I suggested that it may be time to focus on the down-ticket races and not the presidential contest, especially in states like Iowa where Barack Obama has a big lead on John McCain. Sam Wang of the Princeton Election Consortium has made the same argument in a more scholarly way. Volunteer and financial resources are better spent on close races where a little extra could make a difference.

When I’ve discussed this issue with some Obama supporters, they object that it’s important for Obama to win with a big mandate, so he can accomplish more during his presidency. I have never found that argument very persuasive, because even if he has a huge margin of victory, I expect Obama to compromise and move halfway toward the Republican position on many issues. I just don’t believe he has the personality of a Lyndon Johnson, who used his mandate to push big reforms through Congress, bills that changed this country forever. I see Obama as a conciliator who won’t want to rock the boat in Washington.

However, I find myself agreeing more with a different argument for continuing to focus on the presidential race.

Almost every time I turn on the radio I hear some ad from McCain/Palin or the Republican National Committee about “Congressional liberals” or Obama wanting to take your money and spend it on big government programs. Most of these commercials are based on claims that have been debunked by a dozen fact-checkers (like the idea that Obama would raise taxes on families making only $42,000 a year).

Republicans are also paying for sleazy robocalls saying Obama doesn’t want to protect children from criminals and doesn’t want to jail rapists and murderers. This follows an extensive robocall campaign hyping Obama’s very tenuous link to William Ayers (formerly of the Weathermen).

A new direct-mail piece paid for by the Republican National Committee claims Obama thinks terrorists “just need a good talking to.”

Republicans are taking every cliche they’ve used against Democratic presidential candidates for 30 years and amping them up to new levels of deceit.

It’s not enough to narrowly defeat this slime.

A crushing victory for Obama in a high-turnout election would send a strong message that Americans reject these scare tactics. It would also demoralize the Republican elite and donor base who count on this kind of messaging to win elections. They don’t have many other tricks in their book, because their policy agenda is out of step with the values of most Americans.

So go ahead and work toward a bigger landslide than Obama needs, in Iowa and across the country.

But don’t forget to GOTV for our down-ticket candidates too.