They had hearings in relevant Senate and House committees. Kerry, Hagel and some military leaders all appeared. The SFRC narrowly approved it and the vote was to go to the full body, where it quickly was seen as likely to fail. The measure had nay sayers on both sides - with the McCain led group of Republican interventionists against it because it was too limited and many Democrats (and Rand Paul) against it because of fear it could pull us into another full fledged war.
Also different, President Obama adressed the country with a speech explaining what happened and his reasons for wanting to respond and outlining - with no specifics - what he intended to do. At Obama's request, Kerry also gave a speech giving the humaunitarian intervention reason for responding. I believe that Powers also put out a compelling statement. In contrast, Trump made a rather strange, very short comment saying he had ordered the action as (or after ) it started.
Obama did not intionally say that he wanted or needed Congressional approval. That happened a few days later after the British Parliment voted their joining us down. CoS McDonough and Obama made the decision to step back and ask Congressional approval, retaining their postion that the President did not need approval. The latter was tricky for the administration members who testified to Congress.
It was BEFORE the full House or Senate vote that Kerry made the comment when asked how Syria could avoid an attack, that Assad could give up his chemical weapons. Russia, which had not been willing to pressure Syria to do so before - immediately took the administration up on the offer. It took a few weeks to negotiate -- and a Kerry/Lavrov intervention with their UN teams to get an agreement at the UN.
Though much has been made that this was Obama "not doing anything", I suspect that had we done the type of attack Obama spoke of - much like what Trump did - it might have made Assad feel the cost was too high to use chemical weapons, BUT those weapons would have stayed in Syria. From accounts from 2014, they removed at least 600 tons of chemical weapons. Had they not been removed in 2014, can we be sure that none were in places overrun by ISIS later that year? It is never a bad idea to destroy 600 tons of chemical weapons (which the US did) - especially in an unstable country.
As to the nonsense that it failed because Assad clearly had chemical weapons recently (and likely now) -- well, he clearly has at least 600 tons less than he did. Additionally, he may have been able to obtain new CW in the last three years.
Syria was not a success for anyone, but it is absolutely not clear if there was ANY good or even not bad alternative.
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