A CNN contributor and Democratic strategist weighed in on what President Joe Biden needs to say in his speech at the Democratic National Convention in Chicago. Biden is scheduled to speak in a prime-time slot Monday night at the convention, which just two months ago was set to be his coronation as the party’s repeat nominee. But following a disastrous debate performance, Biden dropped out of the race and endorsed Vice President Kamala Harris to take over the top of the ticket. As such, he may have to walk a tightrope Monday night — highlighting his own accomplishments while lifting up his vice…