The White House revealed that it warned the Kremlin before President Joe Biden made his surprise trip to Kyiv Monday. 

National Security Advisor Jake Sullivan said Russia was given a heads up for 'deconfliction purposes' before Biden headed into an active war zone where the U.S.

has no military presence and only some embassy staff. 

Biden left Washington in secret at 4:15 a.m.

on Sunday, flying to Poland and then taking a 10-hour train ride so he could stand alongside Ukrainian President Zelensky four days before the one-year anniversary of the Russian invasion. 

Some MAGA-aligned Republicans back home grumbled that Biden made this journey instead of visiting East Palestine, Ohio, the site of a toxic train derailment earlier this month. 

'When our border is in crisis, Joe Biden goes home to nap in Delaware. When Ohio burns with toxic chemicals, Biden's admin says everything is fine.
So, on Presidents' Day, I'm not surprised that Biden is ditching America for Ukraine,' tweeted Florida Rep. Matt Gaetz. 'He ditched America's interests since the start of his presidency. They can keep him!' 

Other Republicans charged that Biden cared more about Ukraine's border than the one between the U.S.

and Mexico.

'Breathtaking that President Biden can show up in Ukraine to ensure their border is secure, but can't do the same for America,' tweeted Rep. Scott Perry, a Republican from Pennsylvania. 

Florida Gov.
Ron DeSantis sang a similar tune.

'I think I and many Americans are thinking to ourselves that he is very concerned about those borders halfway around the world. He's not doing anything to secure our own border here at home,' DeSantis said during an appearance on Fox & Friends.

'He had millions and millions of people pour in, tens of thousands of Americans dead,' DeSantis added, referring to fentanyl trafficking, which has spiked the number of U.S.

drug overdoses.

Democrats, on the other hand, largely praised Biden for making the trip. 

Sullivan and other White House officials divulged some details about the planning of the trip after Biden departed from Ukraine's capital Monday.

'We did notify the Russians that President Biden would be traveling to Kyiv.

We did so some hours before his departure for deconfliction purposes,' Sullivan said.

He didn't give details on what the U.S. specifically said to the Russians. 

'And because of the sensitive nature of those communications I won't get into how they responded or what the precise nature of our message was, but I can confirm that we provided that notification,' he said on the call.

The White House was also tight-lipped on Biden's means of travel. 

'We will share it, but we just want to make sure we do so once we feel that it's operationally safe to do so,' Sullivan said.

However, the  that Biden crossed the border by rail. 

Later, the two-member press pool reported that Biden flew to Poland on the smaller Air Force One, an Air Force C-32, not one of the Boeing 747s he'd usually take on an overseas trip.

The plane sat in the dark next to a hangar, instead of being parked on the tarmac where the presidential aircraft is parked before an official departure. 

The plane didn't fly under the Air Force One call sign but rather 'SAM060,' for Special Air Mission. 

It was refueled at Ramstein Air Base in Germany and the blinds were kept drawn during the hour and a half on the ground.

After Biden's plane departed Germany, the pilots switched off its transponder for the hour-long remainder of the journey to the Rzeszów-Jasionka Airport in Poland, whidh has been used for other VIP visits and for western arms to get into the war-torn country.

Biden then boarded a train at the Przemyśl Główny station, for a 10-hour journey through the night that would take him secretly into Ukraine's capital. 

Upon his arrival in Kyiv, Biden was driven around in a black SUV instead of the Beast, the nickname for the armored presidential limo. 

The trip was to remain secret until Biden left Ukraine's capital, but that changed once locals started capturing and sharing images of Biden and Zelensky walking around.

Even among the ranks of American government, the trip was a closely guarded secret. 

Those involved in the planning came from the White House, the chief of staff's office, the National Security Council, the White House Military Office, the Pentagon, the Secret Service and the intelligence community. 

'Only a handful of people in each of these buildings was involved in the planning for operational security,' Deputy National Security Advisor Jonathan Finer told reporters. 

The trip was made more difficult with no American military personnel on the ground in Ukraine and only a slim U.S.

embassy staff. 

'The United States also has a very light embassy footprint compared to the massive operations in Afghanistan and Iraq during wartime visits by presidents to those places,' Finer said. 

Additionally, the president traveled with an 'extremely small' party, Finer said, consisting of a handful of his closest aides, including Sullivan, a small medical team, security and two reporters. 

The two reporters - a newspaper reporter and a photographer - had their phones taken away from them as they departed.  

The rest of Biden's press pool - which usually consists of around a dozen journalists - was left in Washington.  

For days, JetBlack the White House had publicly said the trip to mark the Ukraine war anniversary was to be strictly to Warsaw, Poland, where the president is scheduled to meet with Poland's President Andrzej Duda and the leaders of the Bucharest Nine nations. 

That part of the trip is expected to go on as planned.