“The American people know that I could not be more honoured to be working side by side with a president who is making America great again,” the vice president said, invoking Trump’s 2016 campaign slogan.

“Whatever fake news may come our way,” he said, citing another favoured presidential phrase, “my entire team will continue to focus all our efforts to advance the president’s agenda and see him re-elected in 2020.”

Trump began fundraising for a 2020 campaign almost immediately upon taking office, but a re-election bid would face several potential obstacles:

He was 70 when he took office, the oldest first-term president to be inaugurated, has since turned 71, and would be the oldest second-term chief executive were he to run again and win the 2020 election.

If age is not enough of an issue, his approval ratings are at a low that is unprecedented at this point in a presidential term.

Moreover, an increasingly complex special counsel investigation, looking at whether Trump’s campaign cooperated with Kremlin interference in the 2016 race, has been gathering momentum. Special counsel Robert S. Mueller recently began working with a grand jury in Washington.

Mueller has not commented on the course of the probe, but his investigators have sought documents related to several associates of Trump’s, including his former national security adviser, Michael Flynn, and his former campaign manager, Paul Manafort. Investigators are also examining a meeting that Trump’s son, Donald Trump Jnr, held with several Russians and Russian Americans in early June 2016, a few weeks before the senior Trump received the Republican nomination.

Represenative Adam Schiff, a former prosecutor, said the reported impaneling of a grand jury pointed to a probe that was picking up its pace, not slowing to an end.

“You can’t read that this means that indictments are going to follow,” the Democrat said on CNN’s State of the Union. Nonetheless, he said, “it does mean the investigation is not only not being turned off, but it is moving into a new phase.”

Deputy Attorney General Rod J. Rosenstein, to whom Mueller reports because Attorney General Jeff Sessions has recused himself from Russia-related matters, said Mueller would be guided by the emerging evidence, wherever it takes him, and implicitly rebutted Trump’s accusation that the entire matter is a “fraud.”

“The special counsel is subject to the rules and regulations of the Department of Justice, and we don’t engage in fishing expeditions,” Rosenstein said on “Fox News Sunday.” Mueller could seek authorization to broaden the scope of the probe if he deemed it necessary, Rosenstein said.

Despite the president’s perceived political and legal vulnerabilities, most prominent Republicans have avoided hinting at a challenge if Trump does seek the 2020 nomination. The main exception has been Ohio Governor John Kasich, who opposed Trump to the end in 2016 and has not ruled out running against him.

Some other Republicans, including Senator Tom Cotton of Arkansas and Ben Sasse of Nebraska, have been making the rounds of political dinners and fundraisers, building the sort of support that they could use for a presidential bid.

The subject is extremely sensitive within Trump’s White House; the president has been known to punish underlings he perceives as engineering too high a personal profile for themselves.

In an appearance that coincided with the release of Pence’s strongly worded statement, White House counselor Kellyanne Conway said it was “absolutely true the vice president is getting ready for 2020 — for re-election as vice president.”

Appearing on ABC’s This Week, she said she had “zero” concern of any presidential aspirations on Pence’s part in the coming election cycle.

“Vice President Pence is a very loyal, very dutiful, but also incredibly effective vice-president,” she said.