Would a Catholic political party be a good thing?

My short answer is no, and what follows is a brief justification of this answer.

Christ's Kingdom is, as He says in today's Gospel, "not of this world." We are called to build Christ's Kingdom on earth not by ruling the secular realm and enforcing Christian morality and charity with the force of law, but by living out of vocation as Christians and winning hearts and minds by word and deed. Christians are called to transform society from within - we are "the salt of the earth," ideally bringing out the best in all of our various communities. In this way, Christians do not need the secular law to be successful. I do not mean to imply that the secular law is not necessary for social order; it is clearly a fundamental component of the common good. Catholics do and ought to work for the common good in our political life, but we should not seek this good in the name of Jesus. He Himself did not establish a political party or an Earthly kingdom. His Kingdom is "not of this world," and it is our task as Christians to build this Heavenly kingdom here on Earth. The Heavenly kingdom is not one of coercive political force, but freely given sacrificial Love.