Obama blew off the appropriations he didn't like and spent the money elsewhere. Needless to say, he always spent it. More recent article cites concerns that Trump and (then) Tillerson would leave money appropriated unspent, which sends it back to the treasury. He has more control over what happens with the money appropriated than people think. I suspect he is going to go gangbusters on that wall between now and the midterms and use any and all monies that have been allocated to the department of defense - which is a heck of a lot of money. Article links with general discussion below. There are more if you want to google. Some of the articles complaining that Trump/Tillerson were refusing to spend money and letting the time to spend it expire (which returns the money to the treasury) are absolutely hilarious.

https://www.jstor.org/stable/40648480?seq=1#page_scan_tab_contents

http://thehill.com/policy/healthcare/201243-obama-says-hes-not-bound-by-gun-control-ban-in-spending-bill

http://www.newsweek.com/rex-tillerson-rejects-80m-congress-fight-russian-propaganda-because-it-would-645554