President Trump.

Stormy Daniels is but a sideshow in the minds of investors in the stock market. 

The major stock market indexes have given up all the gains posted since November as the Trump policies that have boosted stocks - lower taxes, lax regulation and a crippled labor movement - have been stepped on by Trump the policy-maker, who is starting a trade war with China, persisting in a fiscal feud with his own party, and promoting advisers who are advocates for real wars in the Middle East and on the Korean peninsula.

The Dow Jones Industrial Average fell more than 400 points on Friday, a day after slumping by more than 700 points after President Trump moved to slap tariffs on up to $60 billion worth of China-made goods and China reciprocated by saying it would target imports from the United States. Stocks had their worst week since January 2016, and the Dow is on pace to post its worst month since August 2015.

The Nasdaq fell below 7,000 points for the first time since Feb. 12, led by Action Alerts Plus holding Facebook (FB - Get Report) - down 14% for the week -- but joined also by Alphabet (GOOG - Get Report) and Apple (AAPL - Get Report) , which are now both down for the year.

The big banks tumbled on signs of a trade war, even though interest rates are rising. A trade war heralds lower economic activity, meaning fewer loans, which are generally bad for banks. Citigroup (C - Get Report) fell 3.4%, Bank of America (BAC - Get Report) slipped 4.5%, Wells Fargo (WFC - Get Report) lost about 3% and Action Alerts Plus holding JPMorgan (JPM - Get Report) dropped by 2.6%.

Automakers fell as trade war fears and the possibility of steel and aluminum tariffs raised concerns about higher prices and lower profits. Ford (F - Get Report) lost 1.8%, General Motors (GM - Get Report) fell 3.2%, Fiat Chrysler (FCAU - Get Report) slipped 1.4% and Toyota (TM - Get Report) lost 2%.

The good news, if that's the right term for it, came from defense stocks, presumably boosted by President Trump's decision to hire John Bolton as National Security Advisor. Bolton is known as a hard-liner when it comes to foreign policy, and has advocated the U.S. starting a war with Iran over their nuclear capabilities and making a first-strike on North Korea because, of course, it can.

Lockheed Martin (LMT - Get Report) , maker of the F-35 jet fighter plane and the world's leading defense contractor rose 2.9%. Northrup Grumman Corp. (NOC) rose 2%, Raytheon (RTN - Get Report) gained 2.6% and Boeing (BA - Get Report) rose about 0.5% even though everyone's freaking out about whether China will cut their orders in a trade war. Turns out that China needs too many planes to meet its commercial aviation challenges, and Airbus, the only other major manufacturer besides Boeing, can't make enough of them.

The president's evident unhappiness with fellow Republicans, who presented him with a $1.3 trillion spending bill that few of them had read, led him to issue what turned out to be an empty threat to veto the measure. It was another reminder of how mercurial and unpredictable the President is. It's almost as though he cares more about whether he's dominating the news cycles than he does about providing a steady hand as leader of the world's biggest economy and largest nuclear superpower.

And for investors, that could prove troubling as we enter April. 

Watch TheStreet's founder Jim Cramer discuss a potential trade war with China below.