LONDON—The U.S. dollar fell for a second day on Wednesday as investors became less worried about the risk of Russia invading Ukraine and awaited the release of minutes from the U.S. Federal Reserve’s January meeting. European equity markets were mixed, having rallied on Tuesday after Russia said it would withdraw some troops from Ukraine’s border. U.S. President Joe Biden said more than 150,000 Russian troops were still in a “threatening position” and NATO urged Moscow to prove it was pulling back. Ukraine said the online networks of its defense ministry and two banks were hit by a cyber attack. In currency markets, the moves were small. The U.S. dollar index edged lower and was down 0.2 percent on the day at 95.847 by 1213 GMT. “More optimism around a diplomatic solution in Ukraine may keep applying some pressure on the dollar and the other low-yielders today,” ING FX strategists wrote …