* Futures down: Dow 80 pts, S&P 9.5 pts, Nasdaq 18 pts
By Yashaswini Swamynathan
May 17 (Reuters) - U.S. stock index futures tumbled on Wednesday amid fears that a fresh controversy around President Donald Trump could derail his ambitious pro-growth agenda.
* According to reports, Trump asked then-FBI Director James Comey to end a probe into former national security adviser Michael Flynn, raising questions of whether obstruction of justice charges could be laid against the president.
* The news comes on the heels of a tumultuous week at the White House when Trump unexpectedly fired Comey and then disclosed classified information to Russia's foreign minister about a planned Islamic State operation.
* The developments could distract Trump from pursuing his proposed policies such as tax cuts and simpler bank regulations, which have underpinned a record-setting rally on Wall Street.
* The dollar index retreated on Wednesday, erasing all of the gains inspired by Trump's business-friendly stance after his November election victory. The euro hit its highest level since Nov. 7.
* Bank stocks including Goldman Sachs and Bank of America, which have outperformed in the post-election rally, were off 1-2 percent in premarket trading.
* Among other stocks, Target was up 5.2 percent at $57.37 after the big-box retailer reported a smaller-than-expected drop in comparable sales.
* AbbVie slipped 2.8 percent to $65 after Coherus BioSciences received a favorable patent ruling against AbbVie's Humira drug. Coherus shares rose nearly 7 percent to $23.55.
* Colgate-Palmolive was up 3.6 percent after the New York Post reported that the toothpaste maker's CEO had recently signaled he would be open to sell the company.
Futures snapshot at 6:56 a.m. ET:
* Dow e-minis were down 80 points, or 0.38 percent, with 42,350 contracts changing hands.
* S&P 500 e-minis were down 9.5 points, or 0.4 percent, with 239,478 contracts traded.
* Nasdaq 100 e-minis were down 18 points, or 0.31 percent, on volume of 52,218 contracts. (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Saumyadeb Chakrabarty)