Senators are urging Trump to stick with F-35s as the US eyes buying new souped-up F-15 fighter jets:

The US Air Force will reportedly ask for eight new Boeing F-15 fighter jets in its next budget request, and Republican senators are already worried this could mean bad things for the US's F-35 Joint Strike Fighter.

President Donald Trump has long come across as skeptical of the F-35 and its promises to fool enemy radar and revolutionize aerial combat.

Boeing has responded by offering up an improved crop of old-school dogfighter jets, and the Air Force is interested,Bloomberg reported on Tuesday.

Republican Sens. John Cornyn, Ted Cruz, Susan Collins, Marco Rubio, and Lisa Murkowski sent a letter to Trump warning against buying new F-15s from Boeing, saying it risked US national security by taking away from F-35 buys.

Before even taking office, Trump tweeted that the "tremendous cost" of the F-35, the most expensive weapons program in history, had caused him to look at Boeing.

Now, Boeing has offered up an F-15X, or a 21st-century restart of the Cold War-era fighter jet. Boeing's F-15 was one of the fastest jets ever built and ruled the skies as the US's top air-superiority fighter for decades until the F-22 came online.

Today, Boeing promises a new F-15 with better computers and avionics, and an incredible capacity for 12 air-to-air missiles. By contrast, the F-35 has a shorter range and can carry a maximum of only four air-to-air missiles in a stealth configuration.

But the senators, citing top US Air Force brass, said the US needs F-35s and can't risk buying older, less-survivable program. 

We are extremely concerned that, over the last few years, the DoD has underfunded the F-35 Program and relied on Congress to fund increases in production, sustainment, and modernization. In order to meet the overmatch and lethality goals laid out in the National Security Strategy, the DoD needs to make these investments in the F-35 to affordably deliver and operate this fifth-generation fighter fleet. The F-35 is the most affordable, lethal, and survivable air dominance fighter, and now is the time to double down on the program. 

Essentially, the senators demanded Trump fully fund the F-35 to get Lockheed Martin, the jet's builder and Boeing's chief rival, to step up production to the full rate, at which point the F-35 could cost as little as $80 million apiece.

"New versions of old F-15s designed in the 1970s-1980s cannot survive against the newest Russian and Chinese fifth-generation fighter and surface to air missile threats, not to mention rapidly developing future threats," the lawmakers wrote.

Trump has been clear that the US needs to build up its military to counter near-peer threats such as China and Russia, rather than old foes such as Middle Eastern insurgents, which the US military prefers to fight with stealth aircraft.

As a non-stealth jet, the F-15 doesn't fit the working hypothesis of how to best kick down Moscow's or Beijing's door, but it may well serve a purpose in a great power war.

The senators cited a price of $100 million per new F-15, but that figure may be well off. The Drive reported that the price of the F-15, which Boeing still produces for international customers, could drop to below any cost ever projected for the F-15.