"undermine the position" is a correct and usable phrase in written English.
You can use it to describe when someone or something has weakened the strength of a given opinion or stance on an issue. For example, "The conflicting data from the study undermined the position of the team that argued for the new policy."
Doing so would immediately undermine the position of the current leaders.
General economic conditions began to undermine the position of the bakufu vassals.
According to this worry, fervent exclusivism doesn't show that universalism won't be true, but it does undermine the position that universalism is revealed in the scriptures.
He said it could undermine the position of minority ethnic officers if it was thought they were not recruited on merit.
It helps to undermine the position of the Serb irredentists, who want to keep their part of Bosnia tied economically to Serbia, in the hope that political union might follow.
The detention and subsequent criminal investigation into the partner of a Guardian journalist threatens to undermine the position of the free press around the world, the editors of several northern European newspapers have warned.
Efforts to check them failed, and they used their influence to undermine the positions of Hunter and King.
"Some of the personal attack levelled against me is a not very veiled attempt to undermine the positions that I have worked on and stood for," Hillary says.
Imposition of steel tariffs and farm subsidies has undermined the position of market reformers in Latin America.
It was credited with undermining the position of then chief executive Bob Ayling, who resigned in 2000.
Productivity improvements eliminated many middle-skilled American jobs just as emerging-market industrialisation undermined the position of low-skilled workers.
