The Democrats under Obama reduced the deficit meaningfully after the financial crisis recovery set in. The deficit went from $1.4T in 2009 to $0.6T by 2016. Part of that was the economic recovery, but there was also both legislation and executive orders that reduced spending and increased taxes.

The Budget Control Act of 2011 capped discretionary spending and cut $1 trillion over ten years, the administration further cut administrative spending by 20% via executive order in 2011. Subsequent actions reduced the deficit by $2 trillion, with 3/4 spending cuts and 1/4 tax increases (e.g. the 0.9% Medicare surcharge and capital gains taxes on earners of >$250k).

I agree with you, though, both parties seem to have stopped trying to reduce the deficit over the last decade, I think in part because it hasn't been rewarded politically at all.