 Under siege from fellow Democrats, former Vice President Biden's campaign is quietly testing the strength of Vice President Kamala Harris against former President Donald J. Trump in a head-to-head survey of voters as Mr. Biden fights for his political future with a high-stakes news conference on Thursday. Wouldn't it be something if they did an old swish-a-rooey where she became the top of the ticket and he became the bottom of the ticket? You know how she got her job? Wouldn't that be interesting?