Attendees of the events describe them as crucial opportunities for scientists from the government, the private sector and academia to exchange research and ideas.
Goitein also cautioned that a resort to emergency powers in the current situation - in the midst of a standoff with lawmakers that has produced a partial government shutdown - could be considered an abuse of the president's power. The visit of the Boeing 747 equipped with a massive telescope used to study the fundamental mysteries of the universe has been canceled.
Trump's visit to the border would come in the midst of what is now a 17-day partial government shutdown centering on a dispute over his demand for more than $5 billion in funding to build a barrier to block migrants, majority from Central American countries, from crossing into the United States.
So while Democrats negotiate with lower-level aides, and even Vice President Mike Pence, there's no reason for them to take any deal or concession seriously until it comes out of the president's mouth.
"I don't know what he's basing this on, but he's faced so many lawsuits when he ignores the law and ignores tradition and precedent and just goes forward without any concern", the Democrat said on CBS "Face the Nation".
"I can relate, and I'm sure the people who are on the receiving end will make adjustments; they always do", Trump told reporters outside the White House.
Trump said earlier on Sunday his border wall can be built of steel instead of concrete if that will help Democrats come to terms in negotiations to reopen the government.
For example, in an emergency, the president is allowed to divert money to military construction projects, which could conceivably include the border wall.
"Emergency powers are meant to be used for emergencies, not to settle political disputes or to shortcut the political process", Goitein said.
Intelligence Committee Chairman Adam Schiff called it a "non-starter".
But he said Mr. Trump hasn't made a decision on that option.
The president told congressional Democratic leaders during a meeting on Friday that he was willing to keep the government shutdown for as long as necessary - possibly months or even years - in order to get the funding he wants. Collins and others are also up for re-election in 2020 from states including Colorado and North Carolina where views on Trump are mixed.
However, the interviewer immediately called her out, citing the government's own information that none of those individuals arrived across the southern border.
House Speaker Nancy Pelosi, D-Calif., in her first sit-down interview on network television since reclaiming the gavel last week, maintained that the goal of Saturday's meeting was to reopen the government and blamed Trump for the continued impasse.
"I am pleased to inform you that I will Address the Nation on the Humanitarian and National Securitycrisis on our Southern Border", Trump tweeted. Last year, he visited San Diego to look at wall prototypes.
If the White House and Congress do not strike a deal by this week's end and the government shutdown continues on Saturday, it will become the lengthiest shutdown in United States history.
The vice president said Mr. Trump is still considering declaring a national emergency to fund the wall unilaterally.
Talks to end the partial USA federal government shutdown will resume on Sunday, President Donald Trump says, as the stalemate enters its third week.
Trump reaffirmed that he would consider declaring a national emergency to circumvent Congress and spend money as he saw fit. Such a move is certain to draw legal challenges.
Speaking to reporters as he left the White House for Camp David, Trump claimed many workers without pay "agree 100% with what I'm doing".
The president said "very serious talks" would continue on Monday, Tuesday and Wednesday of the coming week.
More discussions are planned for Sunday.
US President Donald Trump arguing about border security with Senate Minority Leader Chuck Schumer in the Oval Office in December.
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