The Twitter Inc. account of U.S. President Donald Trump, @realDoanldTrump

The impact of a Donald Trump tweet on the value of assets might be losing its punch, according to a leading economist.

The president has mastered the use of the microblogging site to set the news agenda and pump out headline-style messages to his 53 million followers.

Trump’s Twitter account has rattled markets with nuclear threats to North Korea, a promise to enforce tariffs on a huge amount of global trade, as well as warnings over the U.S.’ relationships with countries generally considered allies.

The occasional call for the U.S. and other countries to build infrastructure and raise defense spending has also sent asset managers scurrying to revaluate portfolios.

On Sunday, Trump logged on to Twitter to tell Iranian President Hassan Rouhani that he must “never ever threaten the United States again.”

Tweet 1

The tweet, dramatic with its use of upper case syntax, was in response to Rouhani cautioning Trump on Sunday about pursuing hostile policies against Iran.

In response to the war of words, the price of oil rose slightly. Brent crude climbed back above $74 per barrel as traders factored in a ratcheting up of tensions between Washington and Tehran.

And while U.S. stocks pulled back Monday, the move was hardly major. The Dow Jones Industrial Average fell 18 points at the open of trade while the S&P 500 and Nasdaq Composite traded just below the flat-line.