* Swiss franc hits six-month highs
* Yen rises to highest since April
* Dollar index surrenders 'Trump bump' (Updates to afternoon U.S. trading, adds analyst quote)
NEW YORK, May 17 (Reuters) - The dollar fell by nearly 2 percent against the yen to its lowest level since April and hit a six-month low against the Swiss franc on Wednesday as talk that U.S. President Donald Trump could face the threat of impeachment boosted safe-haven assets.
The dollar index, which tracks the U.S. currency against six peers and had scaled a 14-year peak of 103.82 on Jan. 3, fell 0.6 percent to its lowest level since Nov. 9, surrendering all of its "Trump bump" gains.
News emerged on Tuesday that Trump had asked his now-dismissed FBI chief James Comey to end the agency's investigation into ties between former White House national security adviser Michael Flynn and Russia.
That raised questions about whether Trump tried to interfere with a federal investigation, spurring speculation over the likelihood of an early exit from office for the former businessman.
The dollar fell by as much as 1.95 percent against the yen, blowing through the 111 yen level to 110.93 yen.
The dollar sank 0.75 percent against the Swiss franc, falling to its lowest since Nov. 9.
Traders have traditionally bought those currencies and sold dollars in times of uncertainty.
"Its really a dollar story right now," said Peter Ng, senior FX trader at Silicon Valley Bank in Santa Clara, California. "Obviously it centers around the drama thats going on in the White House thats captivating audiences globally and you can see its causing a risk-off sentiment to the market."
While Wednesday's price action showed the market is losing faith in Trump's ability to push through his campaign trail promises of tax reform and fiscal stimulus, analysts said there was limited expectation he would realistically face impeachment.
Fed fund futures showed the market is pricing in a 69 percent chance the Federal Reserve raises U.S. overnight interest rates at its meeting next month, mitigating losses.
"If the Fed raises interest rates by 25 basis points in June that can and should only make the dollar stronger," said Kevin D. Mahn, chief investment officer at Hennion and Walsh Asset Management. "Youre seeing downward pressure on the dollar because of what's coming out of Washington but thats being offset somewhat by the likelihood of a June rate hike."
The euro hit $1.1155, its highest level since Nov. 9.
It fell 1.3 percent against the yen as investors locked in gains after the euro reached a 13-month high of 125.815 on Tuesday.
(Reporting by Dion Rabouin; Editing by Chizu Nomiyama)