President Donald Trump's impeachment trial heads toward a historic conclusion this week, with senators all-but-certain to acquit him on charges of abuse of power and obstruction of Congress after narrowly rejecting Democratic demands to summon witnesses.

Republican Sen. Lamar Alexander of Tennessee will oppose calling more witnesses in President Donald Trump's impeachment trial, all but dashing Democratic efforts to hear more testimony and boosting odds the Senate will vote imminently to acquit without new testimony, in a matter of days.

Senators faced mounting pressure Monday to summon John Bolton to testify at President Donald Trump's impeachment trial even as Trump's lawyers mostly brushed past extraordinary new allegations from the former national security adviser and focused instead on corruption in Ukraine and historical arguments for acquittal.

President Donald Trump's lawyers plunged into his impeachment trial defense Saturday by accusing Democrats of striving to overturn the 2016 election, arguing that investigations of Trump's dealings with Ukraine have not been a fact-finding mission but a politically motivated effort to drive him from the White House.

Republicans in the Senate appear unmoved by the Democratic push for witnesses in President Donald Trump's impeachment trial despite persistent appeals from Rep. Adam Schiff and the other House prosecutors.