for this you have to take the data of budget deficit and current account balance of payment of at least 30 years and then regress both variables. Make Current account your dependent and budgt deficit your independent. after regression you will see any change in budget deficit how much it affect current account...
You can use a this case the cointegration method or ARDL bound and you must apply the granger causality test to know who cause the other ? and you have more method which you may use as neural network.