Undermine means to try to ruin or block someone's success .
1.The Democrats are always trying to undermine President Trump's plan for a border Wall. The wall still isn't built after two years.
2. Drinking heavily and taking drugs could undermine your chances of a good future career.
3. Hitler's plan for a invasion and takeover in Stalingrad during WW2 was undermined by a terrible snowstorm that winter that made condition for attack impossible.