Technologically we could colonize space using Orion rocket technology. We could have and could still land thousands of people and tens of thousands of tons of supplies and equipment. Making a viable self sustaining colony. It would take a president with 100 times the vision of Kennedy to have done this.
Costs have to come down for space and there needs to be a space based economy.
What is the economy for a moon colony ? Platinum maybe. helium three in the future. tourism.
The orbital economy, space based solar power, tourism and entertainment.
We have a longer wait for more countries and companies to get into the space game. this will make colonization and space more competitive and progress less dependent upon a now quite ineffective US government space program.
Reference on historical colonization.
About 350,000 people migrated to the Americas in the 1600's. 1.5 million in the 1700's. By 1670, There 500 crossings going up to 1500 by 1730. Each of the ships could carry up to 200 or so colonists. Many were moving tons goods back and forth. Various supplies one way and furs and other stuff the other way.
Point being: to colonize space. You have to make a lot of trips (or move a heck of lot of stuff in fewer trips) and move a lot of stuff and live off the resources that are there. Plus there should be economic reasons or strong societal reasons for it.