I'm not sure what you have in mind by "modern politics." But any honest historian will tell you that if you are true historicist — that is, you believe that things in the past shape both the present and the future, and that all people are "products of their time" in some deep and unalterable sense — then you have to know that this applies to you, the historian working today, as well. (In my field this is known as "reflexivity.") One tries to be aware of this and not let it get one into completely indefensible territory.

Not sure if this is what you mean, but with the collapse of the Soviet Union in 1991, the archives of the USSR became (somewhat) open to Western scholars. This has had a massive effect on the study of nearly everything Soviet-related. One example I'll give is related to my own MA work (and I wrote about yesterday regarding sources): Terry Martin's 2001 book The Affirmative Action Empire: Nations and Nationalism in the Soviet Union, 1923-1939 has had a profound effect on the study of Soviet nationality policy. Prior to the opening of the archives, the main discourse on Soviet policy was that it went top-down, and heavily centred on Moscow (see Richard Pipes' The Formation of the Soviet Union, Communism and Nationalism, 1917–1923 for what was effectively the standard on the topic from its publication in 1954 as an example). But these scholars were unable to get into the archives and look at documents, so they had to rely on publicly available works, like Pravda (not that it was taken at face value, but more for the statements it published), defectors, and what other limited information they could glean from the USSR, so it was an incomplete effort.

But after 1991, historians like Martin (who was in the archives throughout the mid-1990s, both in Moscow and Ukraine), were allowed entry to the archives, and thus were able to examine official documents and see that the prior ideas were not fully compatible with what actually happened. As Martin argued, far from being totally within the purview of Moscow, the USSR was very much supportive of helping the ethnic minority groups and worked (at least initially) on promoting locals to positions of power and influence (this changed under Stalin, but is beyond this question). Now ideas like those expressed by Pipes are more or less discounted, while Martin's views are the mainstream

And Martin is just one example. Nearly every Soviet/Russian historian who has published something in the past 20 years has credited the opening of the archives in changing the prevailing view on whatever topic they are writing about. And the best part is that there is so much either unknown to scholars buried in these buildings, or still unavailable for study, so there is so much more we can gain from looking through them, so much more information to study and analyse; all this because Russia allows access (and consider that some of the more repressive post-Soviet states still don't allow foreigners, we can look forward to those one day; I'll cite Turkmenistan here, because Adrienne Edgar's Tribal Nation: The Making of Soviet Turkmenistan, one of the best books on the creation of Soviet nationalities, was hampered by this very fact; she couldn't do research in Ashgabat, which could have had a major impact on her conclusions).