It's all a matter of what you want/need to do with the trailer. If you want to operate the same as you would at a c/g, you need a circuit of #10 wire from a 30 amp breaker ending in a 30 amp RV receptacle. A 20 amp circuit with #12 wire should allow you to run the A/C but very little else.
Regardless of what others have said/done, I would never attempt to run the A/C on a 15 amp/#14 circuit. Even if the breaker stays closed, the voltage drop will likely be too great and possibly damage the unit. You also will quite possibly overheat your house wiring for that circuit, damaging the conductor insulation.
To all of you naysayers, please note that I used the words 'likely' and 'possibly'. There are always exceptions, but I stand by this wording as a professional electrical engineer of 30+ years.