Driverless car deal helps lift Wall Street

Wall Street stocks shrugged off morning declines, closing Wednesday mixed after the abrupt firing of FBI director James Comey signalled more political upheaval to Washington.

Gains in energy and tech stocks helped lead the rebound and propelled the Nasdaq index to a new high of 6,129.14.

The tech-heavy index added 8.5 points, or 0.14%, while the S&P 500 rose 2.7 points, or 0.1%, to 2,399.6.

The Dow Jones Industrial Average dipped 32.6 points, or 0.16%, to 20,921.3.

Shares in Nvidia, listed on Nasdaq, surged more than 17% after the California company reported better than expected profits and announced a partnership with Toyota.

Nvidia, which made a name for itself designing graphics processing chips for the gaming industry, has been working on technology for driverless cars.

Other corporate results weighed on markets.

Shares in entertainment giant Walt Disney fell about 2% after it said it they expected modest growth this year.

Strong growth at Disney's theme parks helped boost quarterly results, which were reported on Tuesday, but those could be at risk if there is broader economic weakness, analysts said.

Meanwhile, Commerce Secretary Wilbur Ross lowered expectations for economic growth this year, saying that the Trump administration's economic agenda was not far enough along to produce a 3% rise in economic growth.

Many economists had already forecast less ambitious growth, but the statement underscored disarray in Washington.

It came amid a backlash over Mr Comey's removal, which is likely to make passage of some of his business-friendly economic initiatives, such as tax reform, more difficult.

Mr Comey was leading an investigation into ties between Russia and US President Donald Trump's campaign. His dismissal provoked strong reaction from Mr Trump's Democratic opponents and also raised concerns among some Republicans.