US President Donald Trump has criticized the Democrats' efforts to oust him by saying the opposition party is trying to oust him because he is fighting for the voters who elected him, noting that the country's future is at stake.

Trump argued that Democrats are doing "one of the greatest frauds in American policy history," and portrayed his accountability inquiry as "part of the opposition party's campaign to remove everything from taking up arms to health care."

"It's very simple. They're trying to stop me because I'm fighting for you, and I will never let that happen," Trump said in a video posted to his 65 million followers on his Twitter page.

Trump's approach signaled a new effort to mobilize his political base to counter the growing threat of his presidency, according to Bloomberg News.

The US House of Representatives has opened an investigation into Trump's accusations of a controversial phone call between him and Ukrainian President Volodymyr Zelinski at the end of July, in which he reportedly pressured the Ukrainian president to conduct investigations that could damage his political rival Joe Biden.