She (smartly, IMO) declines to support taking out Assad because the alternatives available may be more against US interests, and he does not directly threaten the US. IMO, Assad is not an ideological adversary, and because he is a secular leader who values his own life above all else, he can be negotiated with. Tulsi is right on this issue, IMO.
Don't let my comments scare you away from her. I disagree with her on pretty much every issue. I do, however, like her standard for putting US troops in harms way. There must be a strong justification, and it must be in the interests of the United States. Frankly, I think her views align with mainstream Dems on this, but see how the CNN panel is unhappy with her, and even Chris94 is unhappy about her "pro-Assad" behavior.
I also like how she was independent during the primaries last go-round, and stood up for the unfair way Bernie was treated by the DNC.
Link: https://www.realclearpolitics.com/video/2019/02/06/morning_joe_panel_vs_rep_tulsi_gabbard_is_assad_an_enemy_of_the_united_states.html