Among Nixon's other crimes, he cancelled the final Apollo missions.
The whole point of the space station was as a waypoint on the way to lunar bases.
The whole point of the shuttle program was to supply the space station.
So if Apollo is never cancelled we'd have a permenant lunar settlement.
Er...no, we wouldn't. Not to mention that train of logic is totally disconnected from canceling the final Apollo missions, which actually freed up Saturn Vs for building space stations.
Anyways, Apollo was fated to end fairly soon, since it was just the Moon landing program, there was a major budget crunch between the Great Society and the Vietnam War (and Apollo was
very expensive), and Johnson had shut down the Saturn V production line (yes, you read that right,
Johnson). The most that could have happened was flying another J-class mission (Apollo 18), so that there would be a spare available for Skylab.
Congress, not Nixon, had more to do with the ending of AAP and other efforts to use Apollo hardware; they just didn't want to pay for an unlimited space flight program once prestige objectives had been fulfilled, and the programs shorn of their long-range objectives were simply not very compelling (eg., NASA was proposing to use wet-workshops as basically weather satellites, despite the success of far cheaper automated versions).
The purpose for building the space shuttle was more to reduce launch costs from the Saturn V era, which NASA bamboozled themselves and others into believing could actually happen that way with that design.