ANALYSIS — I have told this story before, but it is well worth repeating — that of favorables and unfavorables, and who more often wins an election. 

Shortly after the Democratic sweep of 2006, I spoke to two Democratic leaders in Congress who told me the same thing. It was all well and good that their party had taken control of both chambers of Congress, they said, but what would matter for 2008 — and the next presidential contest — would be how Democrats behaved over the subsequent two years.

Those veteran Democrats insisted that the party needed to show voters it could govern, that it was made up of thoughtful, generally pragmatic people, not wild-eyed extremists who simply wanted to destroy President George W. Bush and return to their tax-and-spend ways.

Democrats face the same challenge today, but they are endangered by a double-pronged attack that makes their task more difficult than it was in 2006.

Also watch: Democrats downplay appearance of disunity on Green New Deal

A perfect foe

Republicans have launched a campaign to redefine Democrats as a gang of radicals who want to undercut basic American institutions and beliefs.

The GOP line goes something like this: These extremists want to turn the United States into Venezuela and destroy democracy and the free market. As House Republican Conference rapid response director Chris Martin wrote recently in a widely distributed e-mail, Democrats are “obsessed with embracing socialism.”

Republicans understand the limits of President Donald Trump’s appeal, and most recognize he won’t change between now and November 2020. They are stuck with an unpopular, tweet-happy president, so the only way to win a second term for Trump is to increase the Democratic Party’s negatives, thereby making its eventual presidential nominee toxic.

I’ve been writing about congressional elections for almost 40 years, and this approach has been standard strategy for decades. When you have a weak nominee and can’t improve his reputation (favorable rating), you try to destroy his opponent (drive up his or her unfavorable rating).

That’s exactly what Trump and the GOP did in 2016, especially after the “Access Hollywood” tape of Trump boasting of grabbing women by the genitals exposed him for what he is.

Republican strategists are well aware that Trump has normally fatal liabilities, so they are going to spend the next year demonizing the Democratic Party as extreme.

That way, no matter whom the Democrats nominate, Trump can paint his opponent with the broad brush of radicalism and socialism.

It’s a good strategy, particularly when it is the only one available. What is the alternative — talking about Trump’s empathy, tolerance, dignity and commitment to inclusiveness?

His supporters don’t need convincing. They adore him. And his critics will never be convinced he is worth supporting. So, the focus of the campaign is voters who don’t like Trump but are worried about what the Democrats might do if they controlled Washington.

Republicans can and will point to the economy to promote the president’s re-election, but 2018 already taught us that a strong economy doesn’t in itself guarantee a winning election for the GOP.

The only strategy available to Republican consultants and talking heads is to make Trump the lesser of two evils — and that means starting off by re-branding the Democratic Party as dangerous, radical, anti-democratic and, yes, evil.

Some free help

The second attack on Democratic leadership’s efforts to prove that the party is ready and able to govern comes from within the Democratic Party itself.

Progressives are angry at Trump and impatient with their own party. They want “real change,” which often means pushing the rhetorical and legislative envelope.

We all understand why progressives are tired of waiting. While Republicans saw Barack Obama as a dangerous radical who wanted to change “our way of life,” liberal Democrats thought him insufficiently aggressive in pushing many issues. Those same Democrats feel as if their agenda has been ignored for years, both by Republicans, who have controlled the White House and/or Congress, and by “establishment” Democrats.

Now, with the country’s demographic profile changing and the Democratic Party no longer dominated by old, white men, party progressives have started to flex their muscles, if only by beginning a conversation about new policy directions.

The mainstream media, fascinated by “firsts,” “isms,” conflicts and personalities, has already been giving outsize coverage to freshman legislators and new voices, as has the conservative media, for very different reasons.

Luckily for Democrats, Speaker Nancy Pelosi has been able to manage her caucus so far.

But the developing presidential race will make it more difficult for leaders to keep the party together and to encourage all voices to remember that anything they say will give ammunition to the GOP.

There is nothing wrong with the various elements of the Democratic Party discussing, and even arguing, about policy options and priorities over the next year, even though some proposals will play into Trump’s hand and the Republican strategy of defining Democrats as a gang of Nicolás Maduro-loving radicals.

But all Democrats best not forget what those two Democrats I already mentioned told me more than a dozen years ago: If Democrats don’t win the next presidential election, then winning Congress (or the House, in the current case) will turn out to have been a much shallower victory for them than it initially seemed.