Conspiracies abound: There was no gas attack; Soros set up the whole thing; Putin told Assad to do a small chemical attack, Trump would send missiles, dismissing collaboration with the Russians. 
My creative imagination thinks Ivanka and Melania were so disgusted that they convinced Trump to avenge the death of babies...beautiful babies. 
Trump did in many tweets admonish Obama for involvement in Syria. 
Campaign promises usually encounter the harsh reality of  being a president. In many cases, all bets are off.