President-elect Donald Trump is already taking credit for the economy.

"The U.S. Consumer Confidence Index for December surged nearly four points to 113.7, THE HIGHEST LEVEL IN MORE THAN 15 YEARS! Thanks Donald!" Trump tweeted Tuesday night.

Consumer confidence, as measured by a business association known as the Conference Board, did rise in December to its highest mark since August 2001.

But is Trump responsible? Probably, but only for the last step of a very long climb.

The confidence index, based on a random sampling of roughly 3,000 people, rose to 113.7 from 109.4 in November. The Conference Board noted a "post-election surge in optimism" for the economy, jobs and stock prices that was "most pronounced among older consumers."

Related: Wall Street's biggest 2017 fear: A Trump trade war

Many Americans are optimistic about Trump's proposals to cut taxes and regulations and ramp up spending on long overdue infrastructure projects. Investors are bullish on Trump's plans too -- though less on his trade threats -- as stocks have hit all-time highs.

But consumer confidence was making a comeback for years before Trump even began his campaign.

In February 2009, in the depths of the Great Recession, the index hit a low of 25.3. Before Trump was elected, it had climbed all the way back to 100.8 in October.

Almost all measures of consumer confidence reported by the Conference Board have improved since the recession. For example, 26.9% of those surveyed in December said jobs were "plentiful." In 2009, that figure was 3.1%. Other measures show a similar rebound.

Related: Trump's tariffs of tax reforms: Which will Congress pick?

In the Rust Belt states that delivered the election to Trump, consumer confidence dipped in December, though it shot up after he won in November.

There's also a darker side to rising consumer confidence: When it's gotten too high in the past, recessions have followed.

In May 2000, consumer confidence soared to 144.7. Less than a year later, the United States was in a brief economic downturn. By July 2007, it had steadily risen back to 111.9. Five months later, the Great Recession began.

No one knows whether a recession this time is around the bend or far off on the horizon. The economy has been growing since June 2009, albeit slowly. But too much of anything can hurt the economy -- even too much confidence.