* Futures down: Dow 40 pts, S&P 1.5 pts, Nasdaq 3 pts
By Tanya Agrawal
March 22 (Reuters) - U.S. stock index futures were lower on Wednesday as investors sought safe haven assets, a day after Wall Street posted its biggest one-day fall since the November election.
* Investors are becoming increasingly worried about the ability of President Donald Trump to deliver on his campaign promises of cutting taxes.
* President Donald Trump on Tuesday tried to rally Republican lawmakers behind a plan to dismantle Obamacare, with Republican party leaders aiming to move the controversial legislation to the House floor for debate as early as Thursday.
* The Republican party leaders can only afford to lose about 20 votes from Republican ranks, or risk the bill failing, since minority Democrats are united against it.
* Some investors fear that if the healthcare reform act runs into trouble or takes longer-than-expected to pass, then Trump's tax reform policies may face setbacks.
* The S&P 500 has run up about 10 percent since the election, spurred by promises that are seen benefiting the economy but valuations emerge as a concern. The benchmark index is trading at about 18 times forward earnings estimates against the long-term average of 15, according to Thomson Reuters data.
* The last time the S&P 500 lost 1 percent or more in a day was on October 11.
* Oil prices also dipped and slipped back to three-month lows after data showed U.S. crude inventories rising faster than expected.
* Gold prices rose to a three-week high and the dollar index , which measures the greenback against a basket of currencies, was at 99.84, near the six-week low of 99.64 reached on Tuesday.
* Economic data expected on Wednesday includes existing home sales for February, which is expected to have fallen 2.0 percent to a 5.57 million-unit rate. The data is expected at 10 a.m. ET (1400 GMT).
* Shares of financials, which suffered their worst daily drop since June, were lower in premarket trading. Bank of America, Goldman Sachs, JPMorgan, Citigroup and Wells Fargo were down. The financial sector has been the best performing of the 11 major S&P sectors since Trump's election, surging 18 percent.
* Sears Holdings fell 5.5 percent to $8.60 after the retailer warned on Tuesday about its ability to continue as a going concern after years of losses and declining sales.
* Dow-component Nike was down 4.3 percent at $55.50, a day after the world's largest footwear maker's quarterly revenue missed expectations.
Futures snapshot at 6:58 a.m. ET:
* Dow e-minis were down 40 points, or 0.19 percent, with 40,762 contracts changing hands.
* S&P 500 e-minis were down 1.5 points, or 0.06 percent, with 208,408 contracts traded.
* Nasdaq 100 e-minis were down 3 points, or 0.06 percent, on volume of 39,863 contracts. (Reporting by Tanya Agrawal; Editing by Sriraj Kalluvila)