U.S. stock index futures pointed to a lower open on Wednesday as traders become increasingly worried about political turmoil involving U.S. President Donald Trump.

Dow futures traded about 150 points, lower, while S&P 500 and Nasdaq futures pulled back 18.75 and 44 points, respectively.

NBC News confirmed Tuesday a report from The New York Times that former FBI Director James Comey put together a memo outlining a conversation in which Trump allegedly asked him to halt an investigation into Michael Flynn, the former national security adviser.

Later on Tuesday, House Oversight Committee Chairman Jason Chaffetz asked the FBI for any records it has on communications between Trump and Comey.

On the data front, the Federal Reserve Bank of New York releases its household debt and credit report for the first quarter at 11 am ET.

On the earnings front, Target target posted better-than-expected quarterly results, sending the retailer's stock 7 percent higher. Cisco Systems, L Brands and ZTO Express are all due to report after the market close.

In Europe, the pan-European Stoxx-600 index was around 0.34 percent lower on Wednesday. In Asia, the Shanghai Composite in China closed 0.26 percent lower, while the Nikkei in Japan closed 0.53 percent lower.

In oil markets, Brent crude traded at around $52.07 a barrel on Wednesday, up 0.81 percent, while U.S. crude was around $48.97 a barrel, up 0.64 percent.