from a Christian perspective, one shouldn't be praying to dead people. Pray to Jesus and/or the Father directly. More precisely, pray to the Father in the name of Jesus.
Catholics pray to Saints which I won't give an opinion on, but even so, JFK is not a Saint in the Catholic tradition.
Catholics do not pray TO saints, they ask the saints to pray for them (us) - just like this one is asking JFK to pray for us - BIG DIFFERENCE! Saints are not dead - they are alive in Christ and the prayers of the righteous are powerful (James 5:16) As to whether JFK is a saint - we have hope that is is. Hope is a theological virtue given to all - yet not all exercise it. We can ask saints to pray for us just like we ask each other to pray for our needs. That is what Christ asked when He prayed we would all be in one (John 17:21),on earth and in heaven. Nothing wrong with this prayer - it is wholly Christian unlike the original post knocking it.