Right Wing Watch has been busy recently:
rightwingwatch.org
The Rise of the Traditionalist International: How the American Right Learned to Love Moscow in the Era of Trump.

The tl:dr version - the combination of Christians (especially Evangelicals but not limited to them), Ku Klux Klansmen, and outright Nazis would naturally gravitate to a murderous ex-KGB agent now in charge of Russia - because he explicitly set up his country to appeal to them.

Everything from weakening Russia’s separation of Church and State and harassing the LGBT (appealing to a wide array of Christian groups, not all of them Dominionists) to presenting his country as the “Last Great White Hope” (attracting the racists), to projection of power in such things as annexing Crimea and parts of Georgia (attracting the Nazis), means it was inevitable these groups would gravitate toward Putin, and because these groups make up a large portion of the Republican base, a large number of Republican politicians are following right along,