You've read it before – and it's true. Markets hate uncertainty.

Failure to pass the American Healthcare Act, which was supported by Republican leaders in Congress and President Trump, may have spooked U.S. stock markets last week.

In an article titled, "How To Make Investing Decisions Based On Politics: Don't," Nasdaq.com reported controversy over the bill was "raising questions about [Republicans'] ability to focus on and pass policies that the market has been eagerly anticipating, such as tax reform and infrastructure spending."  Financial Times concurred:

"The post-election stock market rally has been largely powered by hopes Donald Trump's administration would swiftly launch a bevy of aggressive economic stimulus measures, including tax cuts, deregulation, and infrastructure spending. However, Mr. Trump's difficulty in Congress over the government's healthcare plan has prompted some reappraisal by investors of the prospect of significant stimulus arriving later this year."

Financial Times pointed out it's likely other factors played a role in investors' decision-making, as well. Some professionals have become concerned about market valuations. About 34 percent of fund managers believe global equity markets are overvalued and 81 percent say U.S. equities are the most expensive in the world, reported Fortune Magazine citing Bank of America Merrill Lynch's survey of fund managers.

In addition, estimates for corporate earnings have been revised lower for the first quarter of 2017. Take that with a grain of salt, though. FactSet wrote, "In terms of estimate revisions for companies in the S&P 500, analysts have made smaller cuts than average to earnings estimates for Q1 2017 to date…"

Politics is one factor affecting markets, and partisanship may be affecting consumer sentiment. Richard Curtin, chief economist of University of Michigan Surveys of Consumers, said consumers' expectations about future economic growth were split along party lines in March. "…among Democrats, the Expectations Index at 55.3 signaled that a deep recession was imminent, while among Republicans the Index at 122.4 indicated a new era of robust economic growth was ahead."

We live in interesting times!