You have to remember how big the US is, and laws vary from state to state. There are lawyers who specialize in (US) constitutional law, or practice in federal courts, but generally, someone will be admitted to the bar in just one or two, usually adjoining states. The exception might be lawyers who specialize in something like death penalty appeals, who might be admitted to the bar in Texas and Florida, the states with the most death penalty cases.
Now, someone admitted to the bar in Indiana, who then runs for congress, and wins, is going to end up spending most of his time in Washington, DC. Unless he wants to take time to learn about the law in DC, Virginia, or Maryland, and be admitted to the bar in one of those places, he is going to have a very hard time practicing law in Indiana, and legislating in Washington.
This doesn't mean that he would not serve as a consultant for an old client, say if someone he previously represented in Indiana many years ago has his case taken up by the Innocence Project, and is granted a new trial. He might fly back to Indiana for a week to spend time with the person's new lawyer, handing over all his paperwork and other data on the case, and going over it.
Even if a person is serving in an office in state, though, he may not spend a lot of time in jurisdiction. If someone has a practice in New York City, but is elected to state legislature, and has to be in Albany all the time, he can't keep up with his practice in NYC. And even a mayor of a very small city is going to work too many hours a week to continue a practice.
The only elected job I can think of in direct conflict with being a defense attorney is sheriff, but I really can't see a former criminal defense attorney running for sheriff, and winning.
Now, there are other kinds of lawyers-- patent attorneys, estate planners, and they probably occasionally do things on the side, especially as favors for people, or give advice, and this might mean they have to recuse themselves from legislative votes, but sometimes that happens because of past interests as well. If you were the patent attorney for a drug company, you need to be separate from all previous interests, including selling stock that may have been a perk, if you want the appearance of impartiality when there is some kind of vote coming up involving drug companies and patents. I don't know that there is a law that says you have to, but you don't want your opponent in the next election accusing you of being in the pocket of your former employer.
I'm not sure what your MPs are doing, but it sounds like something not possible logistically, just because of geography, in the US.
Now, someone admitted to the bar in Indiana, who then runs for congress, and wins, is going to end up spending most of his time in Washington, DC. Unless he wants to take time to learn about the law in DC, Virginia, or Maryland, and be admitted to the bar in one of those places, he is going to have a very hard time practicing law in Indiana, and legislating in Washington.
This doesn't mean that he would not serve as a consultant for an old client, say if someone he previously represented in Indiana many years ago has his case taken up by the Innocence Project, and is granted a new trial. He might fly back to Indiana for a week to spend time with the person's new lawyer, handing over all his paperwork and other data on the case, and going over it.
Even if a person is serving in an office in state, though, he may not spend a lot of time in jurisdiction. If someone has a practice in New York City, but is elected to state legislature, and has to be in Albany all the time, he can't keep up with his practice in NYC. And even a mayor of a very small city is going to work too many hours a week to continue a practice.
The only elected job I can think of in direct conflict with being a defense attorney is sheriff, but I really can't see a former criminal defense attorney running for sheriff, and winning.
Now, there are other kinds of lawyers-- patent attorneys, estate planners, and they probably occasionally do things on the side, especially as favors for people, or give advice, and this might mean they have to recuse themselves from legislative votes, but sometimes that happens because of past interests as well. If you were the patent attorney for a drug company, you need to be separate from all previous interests, including selling stock that may have been a perk, if you want the appearance of impartiality when there is some kind of vote coming up involving drug companies and patents. I don't know that there is a law that says you have to, but you don't want your opponent in the next election accusing you of being in the pocket of your former employer.
I'm not sure what your MPs are doing, but it sounds like something not possible logistically, just because of geography, in the US.
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