The White House distanced itself from the indictment of former campaign chairman Paul Manafort and his deputy Rick Gates, as well as a plea agreement involving a former Trump campaign official.
Sanders added the alleged misdeeds have nothing to do with Trump.
But she said it "has everything to do" with Hillary Clinton's campaign and a research firm that produced the dossier of allegations about Trump's ties to the Kremlin.
Sanders was asked about the guilty plea by former campaign adviser George Papadopoulos. She said Papadopoulos was a "volunteer."
Papadopoulos pleaded guilty on Oct. 5 to one count of lying to FBI agents about the nature of his interactions with "foreign nationals" who he thought had close connections to senior Russian government officials.
Papadopoulos was a member of the campaign's foreign policy team. But Trump aides have said he played a limited role in the campaign and no access to Trump.
Meanwhile, Trump's former campaign chairman Paul Manafort pleaded not guilty Monday to charges of conspiracy and money laundering.
Manafort, 68, and business partner Rick Gates, 45, both entered not guilty pleas in a Washington court after being read charges that they hid millions of dollars they earned working for former Ukrainian politician Viktor Yanukovych and his pro-Moscow political party.