Warren may be double-edged sword

US Massachusetts Senator Elizabeth Warren and Democratic presidential candidate Hillary Clinton made their first joint campaign appearance on Monday, finally confirming the previous speculation that Warren would be picked as Clinton's running mate.

For Clinton, to pick Warren as a vice-president will help her gain the support of more progressives who were in favor of Vermont Senator Bernie Sanders.

A recent poll indicates that among 1,200 supporters of Sanders, only 55 percent expressed a willingness to vote for Hillary. This suggests some Sanders' supporters might vote for presumptive Republican presidential nominee Donald Trump if Hillary does not change her image among ordinary voters. The partnership with Warren is expected to reverse the current course, given that the Massachusetts senator enjoys an approval rate no lower than Sanders among ordinary supporters of the Democratic Party.