If we assume that both Cruz and Rubio would behave as president as they did in the Senate, this gives Republicans a basis for comparison. The upside to Rubio is that he clearly knows how to work with Congress and has the potential to move the legislature in a conservative direction. Indeed, he was a policy entrepreneur on the Obamacare insurer bailout, pushing Congress to do something it might not otherwise have done. The downside of this approach is that he might get rolled, either by go-along-to-get-along Republicans or, worse, by liberal Democrats. Something like this seems to have happened with the Rubio-Schumer deal on immigration reform: Rubio miscalculated and put his name on a bill that was too liberal for most of his Republican colleagues.
With Cruz, the upside is that most of the country, Republicans included, hates Congress, and a president who takes an adversarial approach to the legislature might be just what the doctor ordered. On the campaign trail, Cruz has argued that the two parties behave like a cartel within the legislature. This is true. If one looks behind the heated partisan rhetoric, one sees broad bipartisan agreement on what may be called interest-group liberalism: the use of big government to pay off the pressure groups that work the system most aggressively. The best hope for cleaning out the rot is a president who is committed to such reform, and Cruz might be able to embarrass Congress into mending its ways.
The downside is that Congress is a stubborn, recalcitrant institution. This is especially true of the Senate, whose members are noted for their unbounded self-regard. Cruz might be right to castigate them, but will his former colleagues be willing to work with him on reform if he continues to denounce them? If they are not willing, a Cruz presidency might amount to four years of gridlock and a continuation of the ugly internecine battles that have beset the GOP during the Obama years.