'What do I (we) do, if with the passage of time dharma declines and we are attacked by enemies and thieves?'
Bheeshma advocates punishment as the main tool with which to deal with the wicked and action should be prompt.
'Only then will people be afraid and behave well. While you should be soft spoken, your heart should be made of steel and sharp like a sword. Even if there is a treaty with the enemy, you should be vigilant. An enemy is like a snake hiding inside your house and you are always in threat. Hence you should beguile the enemy by talking sweetly to him, by giving him gifts, if necessary by falling at his feet and shedding tears! Once you have charmed him, destroy him, like you smash an earthen pot against the rock, at the first opportunity! There should be no mercy, an enemy has to be eradicated totally! It does not matter, if you regret it later and cry! A thorn which has not been removed fully will pain for a long time. There is a time to be harsh, there is a time to be soft! If you are always soft, people will ignore you. If you are too harsh, there is only fear around you. You have to yield to those who are stronger and to those who are afraid, keep them in fear. Do not develop useless enmities, avoid being overly adventurous, it is like chewing a horn of a cow, there is no juice, no taste, just pain for your teeth. It does not mean you should become timid, you should study the situation well. Be patient like a stork, crafty like a wolf, brave like a lion and be attacking like an arrow! Only then is a king able to control the enemy and achieve his objectives.
Considering the nature of Yudhisthiraa, I thought it was a tall order. So it will be, if I am able to pass this on to our beleaguered PM. But I am sure he would get some solace by trying! The only problem would be to identify his real enemies.