The resignation of retired Lieutenant General Michael Flynn as US national security adviser after only two weeks in office is a significant blow to President Donald Trump's stated aim of greatly improving relations between the United States and Russia.

The move gives a huge boost to the many opponents in Washington to any effort to defuse tensions with Moscow among the hawkish majorities of both the Republican and Democratic parties in Congress, especially in the US Senate.

It will also embolden Trump's determined foes in both Congress and the US media to seek to embarrass and further undermine him by exposing any alleged examples of contact with the Russians that they can find.

The Washington Post reported on Wednesday that leading Senate Democrats had agreed to push for an extended investigation into all possible contacts with Russian government figures that any Trump campaign official had before the Nov 8 US election.

The aim of such an investigation is clear: It is to try and destroy Trump's credibility as US president.

This is an extraordinarily dangerous game. No such effort to delegitimize a new president right after he has taken office has ever occurred in US history.

At the very least, the broad efforts to undermine and delegitimize Trump across the US political establishment will probably succeed in deterring him from making any move to lift the economic sanctions on Russia.

Already, legislation is being prepared in the Senate supported by Republican Senators John McCain, Lindsay Graham and Marco Rubio, all of them unsuccessful presidential candidates and bitter political enemies of Trump, to try and impose a congressional veto over any effort by the president to use his legitimate executive power to end the sanctions.

Indeed, in the current climate, any effort by Trump to lift the sanctions could trigger an all-out attempt to impeach him and remove him from office.

Less than six months after taking power, on June 15, 2001, then US president George W. Bush announced in a speech in Warsaw, Poland, that the United States had to pull the three Baltic states of Latvia, Lithuania and Estonia into NATO as a foreign policy priority, and this was done.

Under Bush, the United States supported the so-called Orange Revolution in Ukraine and other "color" revolutions toppling established governments in other Soviet republics, such as Georgia and Kyrgyzstan.

Barack Obama for all his talk of a "reset" in relations enthusiastically supported the violent toppling of the democratically elected government of Ukraine in February 2014. He also approved an unprecedented NATO military buildup in Eastern Europe.

To have any credibility in Moscow, Trump's neo-detente policy would have to take concrete steps to reverse this dangerous and provocative military buildup. But if he does so, the super-hawks in Congress, led by McCain, Rubio and Graham in his own party, will go all out in their attacks on him.

Russia genuinely wants improved relations with the United States, but the Russian list of demands before this can happen is very clear: Trump would have to end and reverse the US military buildup in the NATO member-states of Central and Eastern Europe, especially the three Baltic states. He would also have to end US support for the current governments of Ukraine and Georgia. Economic sanctions on Russia would have to be lifted.

It is already very clear that Trump may not be allowed to do any of these things, however much he personally might wish to.

The author is a national columnist for the Post-Examiner online newspapers in the US and senior fellow of the American University in Moscow.