The Kremlin's Candidate (Red Sparrow 03) by Jason Matthews

The “exciting conclusion” (Entertainment Weekly) in the New York Times bestselling Red Sparrow Trilogy has Russian counterintelligence chief Dominika Egorova and her lover, CIA agent Nate Nash, on the hunt for a Russian agent working in the US government.
With a plot ripped from tomorrow’s headlines, Jason Matthews is “one of America’s most readable spy novelists” (The Washington Post Book World), and his high-powered, seductive third novel not only continues the dangerous entanglements of Dominika and Nate but reveals with chilling authenticity how Russian espionage can place agents in the most sensitive positions of power. The Kremlin’s Candidate opens with Russian president Vladimir Putin planning the covert assassination of a high-ranking US official with the intention of replacing him with a mole whom Russian intelligence has cultivated for more than fifteen years.
Catching wind of this plot, Dominika, Nate, and their CIA colleagues must unmask the traitor before he or she is able to reveal that Dominika has been spying for years on behalf of the CIA. Any leak, any misstep, will expose her as a CIA asset and result in a one-way trip to a Moscow execution cellar. Ultimately, the lines of danger converge on the spectacular billion-dollar presidential palace on the Black Sea during a power weekend with Putin’s inner circle. Does Nate sacrifice himself to save Dominika? Does Dominika forfeit herself to protect Nate? Do they go down together?