President Biden’s re-election campaign had $71 million on hand at the end of February, more than double the $33.5 million in former President Donald J. Trump’s campaign account, as Democrats continued to expand their fund-raising advantage over Republicans in the presidential race.The cash disparity was detailed in filings with the Federal Election Commission on Wednesday, when campaigns and some presidential committees had a deadline to file fund-raising and spending reports for February.Mr. Trump did pad his campaign’s account in February, adding more than $3 million to the cash on…