By Chris Matthews

The most important political data point for investors to monitor when considering tax and spending negotiations is this Congress, according to Spencer Perlman, a healthcare policy analyst with investment adviser Veda Partners.

"There's functionally no real majority in the House of Representatives, as there's very little that 218 Republicans can agree on," Perlman told MarketWatch. "It only takes three malcontents to throw the sand in the gears of anything."

The Trump administration didn't immediately respond to a request for comment.