Daniel (in Daniel chapter 10) was met by an angel who said to him: "Do not be afraid, Daniel. Since the first day that you set your mind to gain understanding and to humble yourself before your God, your words were heard, and I have come in response to them. But the prince of the Persian kingdom resisted me twenty-one days. Then Michael, one of the chief princes (angels), came to help me, because I was detained there with the king of Persia. Now I have come to explain to you what will happen to your people in the future, for the vision concerns a time yet to come.” So, clearly there are angels that are stronger than others, and as they battle the enemy and his minions, they can be “delayed” but there’s no Scripture that says they are overcome or defeated by satan or his demons.
To me, the most important thing for us to know is that without Christ, we can be easily defeated (and targeted) by satan or his demons, but in Christ we are completely safe. His power is so much greater that it’s hard for our little minds to even grasp it.
Make sure you have on the Armor of Christ in Eph. 6:10-18 - *“Finally, be strong in the Lord and in his mighty power. Put on the full armor of God, so that you can take your stand against the devil’s schemes. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. Therefore put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground, and after you have done everything, to stand. Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place, and with your feet fitted with the readiness that comes from the gospel of peace. In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. Take the helmet of salvation and the sword of the Spirit, which is the word of God.” *