I remember the news at the time.
the build up.
"you know Syria have all these chemicals weapons, if he were to ever use them what would the response be", "this would be a red line".
1 week later....
Syria have used chemical weapons.
Your timeline is wrong. I'll fix it for you.
2012
Obama issues his 'red line' ultimatum: 'We have been very clear to the Assad regime, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilised. That would change my calculus.'
2013
Assad uses chemical weapons in a series of attacks in towns around Damascus, killing ~1,400 people. Obama says the red line has been crossed, and demands intervention: 'If we fail to act, the Assad regime will see no reason to stop using chemical weapons.'
But Congress refuses, so Obama backs down and hopes the Russians will sort it out.
The Russians broker a deal with Assad, who agrees to destroy his chemical weapons stockpile.
This is explicit confirmation by Syria that she does indeed possess chemical weapons.
2014
OPCW confirms that they have supervised the destruction of sarin (581 tons) and mustard gas (19.8 tons) in Syria.
2016
A joint UN/OPCW investigation confirms that Syria used chlorine during chemical attacks in 2014, 2015, and 2016.
2017
Assad attacks rebel forces with a chemical agent in Khan Cheikhoun (UN and OPCW experts late conclude it was sarin). Trump attacks the Syrian military airbase at al-Chaayrate with 59 Tomahawk missiles, after giving the Russians advance warning.
He cites national security as his justification: 'It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.'
This attack is controversial because Trump acted unilaterally.
2018
Assad attacks Douma with chemical weapons. Acting on French intelligence (which confirms the attack and suggests Russian involvement) Emmanuel Macron says his own 'red line' has now been crossed. French forces join a British/American attack on Syrian chemical weapons facilities.