House Speaker Nancy Pelosi said Sunday that senators will "pay a price" if they block new witnesses in Donald Trump's impeachment trial, but the president quickly retorted that she and House Intelligence Chairman Adam Schiff should also testify.The House plans to vote this week to transmit the articles of impeachment to the Senate for the historic trial on charges of abuse of power and obstruction of Congress over Trump's actions toward Ukraine. It will be only the third impeachment trial in American history."It's about a fair trial," Pelosi told ABC's "'This Week." "We've done our job. We have defended the Constitution of the United States. We would hope the Senate would do that as well." She warned: "Now the ball is in their court to either do that or pay a price."Trump tweeted right before and after Pelosi's appearance, in both instances using derisive nicknames. He said both she and Schiff should appear in the Senate for testimony."He must be a Witness, and so should she!" Trump tweeted.The president also rebutted Pelosi's suggestion that no matter what the Senate does, the House vote last month means Trump will be "impeached forever" and "for life.""Why should I have the stigma of Impeachment attached to my name when I did NOTHING wrong?" Trump tweeted, calling the House action a "totally partisan Hoax.'"It is unlikely that the Republican-controlled Senate would call either Democrat to testify in the president's impeachment trial, which could start as soon as this week. The Democratic-run House is set to vote this week to send the articles of impeachment after Pelosi ended a more than three-week delay.Senate Majority Leader Mitch McConnell, R-Ky., seeking a speedy trial to acquit the president, is reluctant to seek more witnesses.McConnell has proposed a process similar to the last presidential impeachment trial of Bill Clinton in 1999 that would start the proceedings and then vote later on hearing new testimony.One leading Republican, Sen. Lindsey Graham of South Carolina, has already predicted that the trial would end "in a matter of days.''In a Fox News Channel interview on Saturday, Graham dismissed Pelosi's tactics, saying the delay would have no effect on calling new witnesses or the expected outcome — acquittal by the GOP-controlled Senate."The Senate should not reward this behavior by the House," said Graham, chairman of the Senate Judiciary Committee. "The Senate should end this trial as quickly as possible. That's what I intend to do. He will be acquitted. I hope and pray every Republican will reject what Nancy Pelosi did, and we'll pick up a few Democrats.'' Top Democrats defended Pelosi's decision to delay sending the articles of impeachment against the president, saying it produced new potential evidence and turned public attention on the upcoming trial."One of the things that holding on to the articles has succeeded doing is fleshing out McConnell and the president's desire to make this a cover up," Schiff said on CBS' "Face the Nation." "If McConnell succeeds in making this trial a trial without witnesses.... That's not a fair trial. That's a sham," he said.Trump was impeached on charges that he abused his power by pressuring the president of Ukraine to investigate Democrats, specifically Trump political rival Joe Biden. Trump was also charged with obstruction of Congress for trying to block the House investigation.While McConnell joined some Republicans in a resolution for votes to dismiss the charges against Trump, at least one Republican up for reelection, Sen. Susan Collins of Maine, said last week she was in talks with colleagues to hear more testimony. Schiff has rebuffed previous calls to testify, saying he was not a fact witness to the events.Pelosi said senators need to consider new witnesses, including former national security adviser John Bolton, who has said he would be willing to testify if he receives a subpoena.Trump is blocking White House officials from appearing and reiterated last week he does not want his former top security adviser to testify before the Senate.House Democrats, who did not issue a subpoena for Bolton last year, did not rule out doing so now."Ït's certainly something that we are considering," Schiff said.Pelosi also left open the door to filing more articles of impeachment against Trump. "It's Sunday morning — let's be optimistic about the future... a future that will not have Donald Trump in the White House, one way or another, 10 months from now we will have an election, if we don't have him removed sooner," she said.Right before Pelosi was set to appear for the Sunday interview, Trump tweeted against Pelosi, calling her a derisive nickname, "Crazy Nancy.''Asked about Trump's tweet, Pelosi said, "Every knock from him is a boost."