2 Possible Currents and Vdrops from same Resistor: Which Will it Be? [Beginner]
If the supply potential is 5V and can delivery up to 3A then a 2Ω load will draw only 2.5A (=5V/2Ω) and still see 5V. 

This may continue if the load is reduced to 1.66Ω (=5V/3A) but any lower may shut down the supply.