Pretty simple. Obama had 59 democrat votes in the senate in January 2009, which would become 60 (super majority) a few months later after a court case was settled to confirm Al Franken had won his senate race. Democrats had two old/sick senators who missed votes at the time (Robert Byrd and Ted Kennedy) which lowered the vote total to 58 often, thus allowing republicans to filibuster. Then of course Kennedy died and republicans won the special election to temporarily replace his seat. Obama still managed to get a lot of legislation through and signed into law.
Dems haven't filibustered Trump much because republicans don't give a fukk about government and have barely passed any legislation. They passed the tax bill, which only needed 51 votes (ie could not be filibustered); any type of tax policy change only needs a 51 majority. They failed to pass the Obamacare repeal bill, which they attempted to pass via reconciliation - a senate tactic that allows you to pass certain bills with 51 votes without filibuster. They did pass a couple coronavirus relief bills, which had bipartisan support. Outside of that, Trump has no legislative victories or "interesting moments." Just the typical spending bills that every president signs yearly.
Dems won the House in 2018 and since then, Trump has basically been a lame duck president when it comes to passing agenda items. He can't do anything unless it can pass the House, meaning the senate doesn't really...do anything.
