When the Senate impeachment trial began on January 21, two things seemed certain -- or at least very, very likely:

Sen. Jeff Merkley (D-OR) criticizes Sen. Lamar Alexander (R-TN) after Alexander said he would oppose calling witnesses in the Senate impeachment trial of President Donald Trump.

Former national security adviser John Bolton, who has been a central figure in Democrats' fight to hear from witnesses in the Senate trial, defended on Thursday Trump administration officials who testified as part of the House impeachment inquiry.

America's latest "national nightmare" will not end when Republicans vote to acquit President Donald Trump of high crimes and misdemeanors, possibly as early as Friday.

Secretary of State Mike Pompeo on Friday highlighted the US commitment to security assistance and diplomacy with Ukraine -- two matters that have been called into question by facts that have come to light throughout the impeachment process that continues to play out in Washington.

A CNN panel discusses Sen. Lamar Alexander's (R-TN) announcement that he would oppose calling witnesses in the Senate impeachment trial of President Donald Trump.

Sen. Lamar Alexander, a retiring Tennessee Republican, said in a statement late Thursday night that he would vote against a motion to hear additional witnesses in the impeachment trial of President Donald Trump.

I have spent the last week glued to the impeachment trial on TV, watching and listening carefully to the presentations of the House managers and President Donald Trump's defense lawyers.

As the senators wrap up their questions in the impeachment trial, the only question left is whether the Senate will vote to call witnesses.

CNN chief legal analyst Jeffrey Toobin challenges President Donald Trump's impeachment attorney Alan Dershowitz over his defense of quid pro quo.