I believe the order is:
1.) The US forms SEATO
2.) Diem and JFK are assassinated
3.) 2 US Navy ships are attacked by Vietnamese torpedo boats
4.) Congress passes the Gulf of Tonkin Resolution
5.) Elections that could have reunified Vietnam are rejected
However, make sure to double check these, as I am not 100% sure about the last one. Albeit, I am almost positive that the other four are correct (in relation to the others, that is). Don't take my answer for fact, this is just a shove in the direction (or so I hope).
Answer:
one that tested and found to be true by peers and colleges
Explanation: