If you jump in , you act quickly, often without thinking much about what you are doing.
The Government had to jump in and purchase millions of dollars worth of supplies.
PHRASAL VERB : V P
JUMP IN
Meaning of JUMP IN in English
Collins COBUILD Advanced Learner's English Dictionary. Английский словарь Коллинз COBUILD для изучающих язык на продвинутом уровне. 2006